View Full Version : Does anyone think cans make AR's act goofy in terms of accuracy?
My precision AR is a hammer. I was out with another member here a couple weeks ago and we laid down a number of 3-4" groups at 600. I shoot it exclusively with a 5" TBAC can.
Last October at the Team Safari in Logan, I had elevation issues. Shots both high and low. There was enough wind that I can't evaluate if I was also seeing accuracy issues there, too, but it's entirely possible. It wasn't just a little off, it was a lot off. At one memorable stage, I was 0.4 off at 350 yards.
I spent from then to now investigating and checking off potential causes. I looked at the scope, barrel fit to the receiver, fit of upper to lower, SD of the ammo, you name it. I looked at every possible cause I could imaging including a bunch of time spent experimenting with my position looking at things like bipod loading and head pressure. Nuthin'.
I just got back from shooting the Team Challenge in Douglas last weekend. I went with high hopes that somewhere in that process I'd identified and fixed the problem. Sadly, I saw a lot of the same stuff. In fact, this time I saw the gun go cuckoo on one stage in particular. I needed a hit on a 12" plate at 450 yards. I put 12-14 rounds on that thing with a good spotter calling my impacts (plus my own observation of the impacts) and could not get a hit. It was the craziest damn thing I've ever seen. I skipped it and hit the next one 100 yards farther out on the first or second shot.
In the end it only cost us a couple of points all weekend as I made up for it with volume of fire, but it's driving me nuts.
Maybe, possibly, it's related to heat. I can't back this up, but my impression is that the gun goes from fantastic to crap as it heats up. My team mate is convinced his AR's don't shoot worth a hoot with a can. I got similar anecdotal input from a couple of other guys at the match.
So my question to you guys is this: Are cans unsuitable for use on a precision AR? If you say yes and think you understand why, I'd love to hear it. If you say cans are fine, tell me if you have experience with long strings of fire and significant heat.
Delfuego
08-08-2016, 17:23
This exact thing was described to me by one of the guys who shot the last AR match in Raton. Once he pulled the hot-ass can off he was hitting steel again. took him quite a few stages to figure it out. He had a TB can and described his AR as a very accurate normally. Could it be barrel heat-up and possibly droop caused by the weight of the can? I don't shoot with a can so don't really know much there.
Since it was a UKD match could it have been a bad range? I have been guilty of that :)
Great-Kazoo
08-08-2016, 18:04
I use a cover on my cans. I also load specifically to the suppressor.
Another observation....... shooters speak highly regarding SMK's. My 1:12 LTR has terrible accuracy, compared to hornady's in the same bullet (168 BTHP) weight, with a can on. How they shoot without, who knows? It's annoying as hell to shoot sans suppressor.
For Zero / groups to see what bullet weight the rifle liked i did 4 - 5 rd mags with bolt open during reload of mag. Then did a 10 round string with little if any variance of grouping.
This exact thing was described to me by one of the guys who shot the last AR match in Raton. Once he pulled the hot-ass can off he was hitting steel again. took him quite a few stages to figure it out. He had a TB can and described his AR as a very accurate normally. Could it be barrel heat-up and possibly droop caused by the weight of the can? I don't shoot with a can so don't really know much there.
Since it was a UKD match could it have been a bad range? I have been guilty of that :)
At some point I'll screw a brake on it and do some testing. Your story is one of many, and at some point I'll be forced to believe the data even if I don't understand the mechanism.
Probably not bad range data. The targets in question were very easy to range, and my teammates confirmed it.
I ran 77g SMKs last October and 69g TMKs last weekend. Superb, accurate loads. I'm fairly certain it's not load related. Oh, I run a cover, too, so it isn't mirage.
Just some data for you.
TBAC 223P-1 on a 20" AR, with a 1/7.75 custom CLE barrel and matched bolt. I shoot hand loaded 69g Nosler custom competition over 23g of XBR 8208. Here are two examples of what happens when I do long strings of fire. I originally noticed the oddity when i was doing some load testing. So I put together a test to see what I could.
In each of these cases I fired 10 very quick rounds at another target to warm up the barrel. Then I fired a single shot at the target below, then 2 quick shots on another target, then back to the target below. Lather, rinse, repeat.
First time it did this:
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So I wanted to figure out why - so I did it again with some measurements.
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Didn't trail as much as the 2nd time - and the only reason I can think why (only difference other than ambient temp which wasn't that big) is due to the attachment of the Magnetospeed to the suppressor for measurements.
In both cases the earlier shots are at the top, later shots at the bottom.
My belief is that this doesn't happen when the suppressor is not mounted. But, the loads are developed for use with the suppressor and I haven't done it, yet, with just an open muzzle.
Take from it what you will.
That's good data there. Thank you.
denverco
08-09-2016, 06:59
I wonder if this isn't necessarily the can but possibly the mounting system the can is using. The M110 and mk12 patterns both use reflex cans and I've never heard of either having accuracy issues.
Have you talked with the guys at Thunderbeast about it yet Tim? Just wondering what they said if so. Can you repeat this issue on other rifles ?
I would think that the weight of the suppressor might affect the resonant frequency of the barrel, and require some load retuning to find the sweet spot accuracy-wise, but I can't come up with a good theory for vertical stringing...
I wonder if this isn't necessarily the can but possibly the mounting system the can is using. The M110 and mk12 patterns both use reflex cans and I've never heard of either having accuracy issues.
In my case above, the 223P is direct thread. Always good and tight.
I do not believe this is a TBAC specific issue, and have yet to experiment with my OBR to see if I have a similar issue.
I saw it on my ARs as well several years ago. With no measureable stringing hot to cold on my heaviest barreled AR, added a suppressor and not only did I get more stringing, a POI shift, but the groups opened up as well when going from cold to hot and hot to cold...or problems when "warm". I spent some time discussing this with John Noveske before he died and he gave me some good intel to work with. After some testing and trying various things, I found a solution that has worked.
I have been able to reduce the stringing and hot shift to a manageable level by going to over 100 ft-lbs of torque (105 in one and 115 in another) and thermal fitting of the barrel extension to the receiver. You are effectively adding a cantilevered weight at the end of the barrel, similar to a point load on the barrel, albeit more consistent than a point load from say a barricade pressure on your barrel. The barrel attachment, loose or tight fit of the extension in the receiver and dissimilar metals will give inconsistent POI vs. POA during the heating process. If everything is pretty good, I can keep consistent groups hot, or cold, with some shift, but not in transition without very high torque levels and a thermal fit barrel extension.
If you have a 6061 receiver, don't bother. You will need a 7075 receiver (the thicker the better) to be able to mitigate the inconsistency during the heating process.
My can is direct thread also. It seems an unlikely failure point, but I've already looked at all the "likely" stuff.
You have seen me run a can on my ARs and run them hard.
No changes to group size. Nice round groups out to 600 yards.
Try SMKs instead of TMKs would be the only think I can think of. The different ogive might be a cause.
Every time I have a problem I remember that you don't. Maybe it's type of can. My rifle does it with both 77SMK and 69TMK loads. Once the SAC is over, I'll do some testing and try to get to the bottom of it. I have to say, there is a lot of anecdotal evidence that many people are having problems. It never shows up at local matches, possibly because the gun never gets hot.
Every time I have a problem I remember that you don't. Maybe it's type of can. My rifle does it with both 77SMK and 69TMK loads. Once the SAC is over, I'll do some testing and try to get to the bottom of it. I have to say, there is a lot of anecdotal evidence that many people are having problems. It never shows up at local matches, possibly because the gun never gets hot.
At an average AR match I will shoot 25-35 rounds in 2-2.5 minutes. The gun and can are plenty hot.
At the past Logan NM matches, both Mike and I both got our guns hot. And we were shooting typical Blue Steel ranch targets/distances.
For our precision matches, neither the gun or can heat up.
Maybe my can being a brake attach SF mini and yours being a direct thread...
Great-Kazoo
08-10-2016, 12:43
My can is direct thread also. It seems an unlikely failure point, but I've already looked at all the "likely" stuff.
I run brakes or f/hiders on my suppressor host. I tried a direct thread on one, it lasted 1 day. IMO a brake, while rude to other when unsuppressed, works very well with can for POI consistency.
I run fmj & bthp for 223 & 308. no issues.
It's certainly possible that SF can is the answer. It's just hard to figure out what aspect of my can is changing with heat.
Or maybe as Mark suggest it's related to extension to receiver fit. I got some input to that effect from a guy who builds high power uppers. He has extensions machined in 0.0002" diameter increments and thermally fits them to the upper. He's also picky about a particular brand of extra rigid upper, though I forget what it was. Some special DPMS, maybe. I tried to address all that last fall by gluing the barrel in; maybe that is insufficient. Thoughts, Mark?
How would an upper that uses bolts to tighten the reciever around the extension do? (Sorry, the name/brand and model of the upper escapes me..)
XC700116
08-10-2016, 14:12
Ok, so I've been seeing the same issue with my 6 grendel, before that my 25dti (which I had chalked up to a fluted barrel) however, I just put together a 223 with an extremely heavy barrel and the most solid barrel to receiver setup I can figure, and in order to fit it, I had to throw the receiver in the oven and barrel in the freezer, and this one doesn't seem to exhibit the issue, but it's testing is minimal. I'm starting to agree with mark on this, at least to an extent, in that it seems to play nicer thus far.
Or maybe as Mark suggest it's related to extension to receiver fit. I got some input to that effect from a guy who builds high power uppers. He has extensions machined in 0.0002" diameter increments and thermally fits them to the upper. He's also picky about a particular brand of extra rigid upper, though I forget what it was. Some special DPMS, maybe. I tried to address all that last fall by gluing the barrel in; maybe that is insufficient. Thoughts, Mark?
The DPMS is this one: http://www.midwayusa.com/product/138383/dpms-upper-receiver-stripped-ar-15-low-profile-matte That is what a lot of high power guys use. It does have thicker walls and is heavier. As far as receiver extension to barrel extension fit, I still had to use shims with that one.
Yes, that's exactly the one he likes. I suppose someone makes an extra sturdy billet upper, but I haven't paid any attention to that whole scene.
I hadn't considered the different thermal expansion rates. That's quite an interesting thought. I did a quick napkin calculation based on an increase in temperature of 100°F. It appears that the diameter of the aluminum upper increases 0.0005" (half a thou) more than the barrel extension. I'll bet the delta T is greater than 100° in a lot of cases. It might approach 3/4 to a full thousandth if you had real numbers and took more than 30 seconds to do the calculation. That's plenty 'nuff to start causing problems, I think.
Very interesting...
I assumed all SS was the same. Not so. 416 moves much less than the alloy I looked up.
Re-running the numbers shows the receiver might grow almost 0.001" larger than the extension with a delta T of 100°F. Could be twice that if it really got hot.
SA Friday
08-10-2016, 16:28
Could it be the barrel extension face on the upper not being trued? This could be a factor too with thermal expansion and contraction. I doubt anyone would ever see it short of these long distance rifles.
I trued mine, but just with the kit Brownells sells. I have no way to measure the result, though the tool is soundly thought out.
XC700116
08-10-2016, 17:25
I assumed all SS was the same. Not so. 416 moves much less than the alloy I looked up.
Re-running the numbers shows the receiver might grow almost 0.001" larger than the extension with a delta T of 100°F. Could be twice that if it really got hot.
Also consider that with a can on a DI setup, dumps more and hotter gases I to the BCG and receiver, just look at how fricken hit the brass is coming out.
Kaiser.Shooter
08-10-2016, 20:28
How would an upper that uses bolts to tighten the reciever around the extension do? (Sorry, the name/brand and model of the upper escapes me..)
You probably meant F&D Defense rifles
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You probably meant F&D Defense rifles
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I did a search last night and found what I was thinking about. LMT has a switch barrel system where the barrel is clamped with 2 bolts going in from the side of the upper. I can't find any details of the upper, but I assume that the upper is tightened around the barrel like a hose clamp. This should be more robust then the nut on an AR that only grabs a flange. It would be a good data point to compare the LMT system to the AR system, and would likely help to point out if the nut is the cause.
Take the can off?
That's the plan. Nice title, BTW.
Delfuego
08-11-2016, 11:29
That's the plan. Nice title, BTW.:) Who taught that kid how to shoot anyway? Making us all look bad...
I'll take some of the blame for that. Self inflicted wounds hurt the worst...
Watched Mike and Mike both at the 1st SRM carbine match both run their rifles , 20 inch barrel with 223P1's , get the guns hot enough to smoke the can covers and make repeatable hits from 240 to 690 on the speed shoot stage .
13 or 14 misses in a row and the a hit at the next target on a UKD match is a range estimation error .
Barrel to receiver fit is huge and a sloppy fit will cause all sorts of problems . JP builds their upper that is thermal fit with both shim stock and red loctite around the barrel extension .
The one year that I ran a can at TBTC I had 0 issues with wandering or group size and that was with a 18 inch barrel and a 1 off 223A brake attach can Shane loaned me .
13 or 14 misses in a row and the a hit at the next target on a UKD match is a range estimation error.
Not in this case. Range was easy to get and confirmed multiple times. Rifle shooter used it for a perfect centered hit. It was pure luck. I'd apparently used up all the bad juju on the previous target.
I keep going back to JP and their process. I'm pretty sure they have it figured out. However, my teammate is an all JP guy, and he has issues with cans on his guns, too.
Not everything with JP on it is thermofit. :)
I use Nordic receivers, who make the JP receivers, and skip the Red locktite. Locktite, on passivated metal, does not cure and on about half of the JPs I have taken apart, is pasty or liquid even after a year or more. But I am a total believer in the thermofit process and high torque levels on quality receivers.
John Noveske used Rockset for the extension fit and that works too...but the receiver and barrel essentially become one and there is no do-over.
I didn't know that. Forged receivers are not thermo fit maybe?
I'll take it, she deserved that one...still stings though haha
*Man card on probation*
Not_A_Llama
08-13-2016, 09:16
Locktite, on passivated metal, does not cure and on about half of the JPs I have taken apart, is pasty or liquid even after a year or more.
Have you tried using Loctite 37509? I'm getting very hard cures on my anodized uppers and stainless barrels (actually, one's that Nordic you helped make)
It oddly actually even works when sprayed on preassembled uppers.. propagating crosslinking?
Have you tried using Loctite 37509? I'm getting very hard cures on my anodized uppers and stainless barrels (actually, one's that Nordic you helped make)
It oddly actually even works when sprayed on preassembled uppers.. propagating crosslinking?
Yes, that is technically a primer that activates the metal allowing a better cure. The curing of locktite is technically a controlled corrosion process which increases slightly in volume. Using the activator/primer is a great way to go. It takes care of the loose fit, it is thermally stable beyond temperatures possible at the chamber. But, like rockset, it really becomes a permanent installation. I tried using it with green applied from both the receiver side and barrel side and it snugged up the fit and helped the thermal drift...but when David came back a few years later with a shot out barrel...we had to go with a new receiver too. Only the handguard and receiver small parts could be reused.
I have a Rockset one I am going to pull apart this winter. I got my wife one of those Sous Vide cookers and I am going to turn that to high and put the upper in a cooler with the cooker running for 24 hours and see if I can take it apart and salvage the upper receiver.
colorider
08-16-2016, 14:47
I have had success getting roksett lot break free with hot water. Soak for a bit and it worked great. This is on muzzle brakes.
Not_A_Llama
08-16-2016, 15:09
I had decent luck undoing a couple loctited receivers with...ok, here goes: a broomstick.
At the end of the day, anodizing is pretty non-porous, as far as loctite's concerned.
This group was shot at 600 yards with a hot gun chambered in 6 Grendel. Right on elevation call, but it was windy.
http://i890.photobucket.com/albums/ac105/puebloshooter/IMG_1466.jpg (http://s890.photobucket.com/user/puebloshooter/media/IMG_1466.jpg.html)
Never had an issue getting any of the uppers I've built apart with anything more than a propane torch to heat the receiver and barrel extension . All were assembled with Loctite 271 and the one that came apart after a month because the barrel was a turd the Loctite was set up solid . Never used accelerator and always have only cleaned with brake clean or acetone .
Haven't tried shim stock and thermal fit yet but the next one will be .
Just my .02 but I'm running a 18" upper with an Allen Engineering AE M5, outside of the POI shift which has been repeatable accuracy has remained consistent. Could be just of the mounting system used by Allen Engineering (AKA Ops Inc.)
Doesn't matter any suppressor is going to have a POI change from an unsuppressed zero . The marketing BS about no zero shift is just that , there is no way that adding give or take a pound at the end of the barrel isn't going to change the harmonics , look at the high end rimfires that tune with weights at the muzzle .
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