Primer Blow Out with NO Over Pressure Signs?

[TheBelly]

Okay, so I decided to try the wood dowel method of measuring the bolt face to the lands again.

I seated a bullet in an empty case (FGMM once-fired in my rifle, BARELY sized the neck so it was a little tight but that I could easily push the bullet deeper by hand). Carefully put the round in the chamber, slowly slid the bolt forward until it stopped, then used a small bungee cord to hold it forward and up. Slid a wood dowel down the barrel until I touched the bullet and marked the dowel. Ejected the round carefully, then slid the bolt face forward again, bolt up, bungee and measured with the dowel again. Here are my measurements:

1 - COAL Before - 2.968"
1 - COAL After - 2.952"

Decided to fully close the bolt this time, and got nearly the same after measurement:
2 - COAL Before - 3.041"
2 - COAL After - 2.950"

Left the bolt in the up position again:
3 - COAL Before - 2.983"
3 - COAL After - 2.955"

I can continue doing this all day, but I have a feeling the COAL base to lands will be 2.950" +/- 0.01", so I have a feeling I am not jammed against the lands. And yes, while I don't have a way to measure the o-give yet by marking the bullet tip with sharpie and looking for the scratch mark from the rifling, it is at least 0.55".

The markings on the dowels are as follows:

1 - 3.015"
2 - 2.955" (closed bolt, not sure if this is accurate though)
3 - 3.016"
4 - 3.022"
5 - 3.010"

What is your magazine OAL?

[J]

Is the rifle 100% stock? Remmy almost always cuts their chambers LONG, to CYA on these types of things. At mag-length I still can't get my bullets as close to the lands as I would like (the 178 AMAX really likes to be 0.010 from the lands) I can get them to about 0,070 and keep it to the AI mag length.

Your chamber measurements are pretty close to what most find in stock Remmy chambers. I shoot a different bullet, so we can't compare apples to apples, but I'm at 2.954 COAL to be at the lands (measured with proper tools). Given the different bullet shape 2.950 sounds perfectly reasonable to me. Though the hornady tool to get a good measurement isn't terribly expensive and would probably be a good investment.

Go back to the low end and try a different batch of primers, powder and bullets and see what you get. It is possible something there was out of spec.

[J]

What is your magazine OAL?

In the B&C that comes on that, WAY too long. I bet he could get over 3.00 in there.

[TheBelly]

In the B&C that comes on that, WAY too long. I bet he could get over 3.00 in there.

Long enough to measure it and get it off the lands .002"?

[J]

If he were so inclined, yes. I'd advise him to get a better measurement before cutting it that close though.

[TheBelly]

I start with jammed into the lands, back it off .005" then find the powder node.

then mess with the jump.

[BuffCyclist]

Nail meet Hammer.


primer cratering is only indicative of one thing: there's a space in the bolt face for the striker to peek through and strike the primer. If there are pieces of the primer breaking/shearing off and ending up in the bolt, then that could be a problem.

my max load is 42.0 grains pushing a 175 gr bullet and a COAL of 2.805"

That’s what I was thinking. Honestly, the cratering I’m seeing is not the usual primer cratering, it is extremely minimal and somehow even the camera picked it up and magnified it.

What's the max length from base of case to ogive that your rifle can handle?

Can’t give you that, don’t have a method to measure the ogive yet, see further down.

One more thing to consider...

Accuracy International rifles have a huge firing pin hole. With just about every mid range load and up, I get cratering.

May moons ago David Tubb blew up an SR-25 in 260 doing load development. The gun came apart but the brass/primer looked fine.

I measure case head diameter in extractor rim cut so I can tell if the pressures are high. Easier than measuring the insides of primer pockets.

This sounds like something I should try to measure and see if there is any noticeable difference.

38.0 - .403 (2nd rd was .410 with the loose primer)
38.4 - .403
38.8 - .402
39.2 - .403
39.6 - .402
40.0 - .403
40.4 - .404
40.8 - .403
41.2 - .403
41.6 - .403
42.0 - .403
42.4 - .403
42.8 - .425 (not reliable because we pried this case out, but impressive)
Once fired case of same year - .404”

I measured the remaining 51 cases and they all measured 0.402-0.404”, so there are no signs of loose primer pockets on any of the other brass. While this method will work for determining after firing if the loads are hot, it does not appear to shed any light on what happened or if any of my other cases are compromised.

It might be simple, but did you calibrate your scale?

Yes, I checked it with my 20g check weight every 5 rounds between changing loads, and also used a 168gr SMK, 180gr pistol bullet and 124gr pistol bullet to confirm.

What is your magazine OAL?

Just measured that. It isn’t a magazine so to speak, but the hinged floor plate that comes stock on Rem 700s.

Rifle Magazine OAL - 2.830” (2.840” would not fit)
Measured by starting with a long case and load into internal magazine (hinged floor plate), then seat a 2.800” dummy round on top. Kept seating deeper until the 2.800” round would insert into the magazine.

I measured the overall length of a bullet again when seating to the lands and found it to be closer to 2.980", however, the bullet is barely held in there (anything longer than 3.010" and the bullet falls out if I look at it wrong).

I got this new measurement by seating bullet to 3.000 or longer, inserting into chamber softly, slowly sliding bolt forward and once the round was centered in the chamber (and not on the floorplate follower), push a dowel rod to touch the bullet. I would then hold the dowel rod loosely so I could feel it move as the bolt slid forward. I would softly tap the back of the bolt with my thumb and once I felt the dowel stop moving, I stopped tapping and pushed the round out slowly with the dowel.

Is the rifle 100% stock? Remmy almost always cuts their chambers LONG, to CYA on these types of things. At mag-length I still can't get my bullets as close to the lands as I would like (the 178 AMAX really likes to be 0.010 from the lands) I can get them to about 0,070 and keep it to the AI mag length.

Your chamber measurements are pretty close to what most find in stock Remmy chambers. I shoot a different bullet, so we can't compare apples to apples, but I'm at 2.954 COAL to be at the lands (measured with proper tools). Given the different bullet shape 2.950 sounds perfectly reasonable to me. Though the hornady tool to get a good measurement isn't terribly expensive and would probably be a good investment.


Go back to the low end and try a different batch of primers, powder and bullets and see what you get. It is possible something there was out of spec.

100% stock. The stock is a HS-Precision, not B&C.

Yes, I currently have these on the way:
Hornady LNL Bullet Comparator
Hornady LNL Overall Length Gauge (with modified case)
Hornady Headspace Gauge for 308 (to measure neck setback when I start neck sizing only)

In the B&C that comes on that, WAY too long. I bet he could get over 3.00 in there.

It’s an HS-Precision and I can fit 2.830” in the Rem hinged floor plate “magazine”.

Long enough to measure it and get it off the lands .002"?

If he were so inclined, yes. I'd advise him to get a better measurement before cutting it that close though.

I start with jammed into the lands, back it off .005" then find the powder node.

then mess with the jump.

So from here I should measure the overall length of the chamber, determine if I can get the bullet jammed (doubt I can and still have the neck tension to hold the bullet). I will also use the comparator to determine the case length from base to ogive and if I understand correctly:

Chamber length equals the measurement from the bolt face to rifling lands. Then, seat the bullet from case head to ogive to be the chamber length MINUS 0.005” (if possible).

Is there a way to determine the maximum length the round should be from case head to o-give for a given bullet? As in, how do I know if there is enough contact between the neck and bullet?



Also, I measured the diameter of some Win LR (WLR) primers and found them to be .210" and spec calls for .2105 minimum. While I don't have a pair of micrometers to measure to the half-thousanth, the needle on my calipers (Mitutoyo ie not Frankford Arsenal or Harbor Freight cheapies) was EXACTLY on .210" and not even a hair closer to .211".

[TheBelly]

Is there a way to determine the maximum length the round should be from case head to o-give for a given bullet? As in, how do I know if there is enough contact between the neck and bullet?

If you have the maximum OAL that your chamber can support, then you can get the 'jump distance' pretty easily.

Seeing as most dies don't load directly off the tip of the bullet, then you can take one round that's loaded to the correct length and just set your dies off of that. This is one of those times that I don't worry about the number too much, other than to make sure that the die doesn't move while I'm loading.

I can explain in better detail, but it takes a long time.

[BuffCyclist]

If you have the maximum OAL that your chamber can support, then you can get the 'jump distance' pretty easily.

Seeing as most dies don't load directly off the tip of the bullet, then you can take one round that's loaded to the correct length and just set your dies off of that. This is one of those times that I don't worry about the number too much, other than to make sure that the die doesn't move while I'm loading.

I can explain in better detail, but it takes a long time.

Thanks Belly, that part I understand. What I was trying to say is, is there a lookup table somewhere that shows the farthest out a bullet should be sticking from the case. As in, what is the minimum amount of contact with the case a bullet can have? Sort of like the book on ogives for all the bullets out there. Example, a 168gr SMK can not be longer than 2.85", a 175gr SMK can not be longer than 2.90", etc.

The rest of my tools should arrive today, but working 14hr days for the rest of this week and next, I won't have time to get to it for a while. I also ordered 100 brand new Lapua cases and will attempt to find some Federal 210 or CCI 200 primers locally. The plan is to pull the remaining 51 rounds, reweigh the charges to ensure they are what I was expecting, then using new primers and new brass, I will load them up again in the Lapua brass and reattempt shooting them at the range.

I am still not entirely sure the problem doesn't lie solely with the LC LR brass, because I have no other explanation (other than powder charges being off which I'll find out when I pull them) as to why the 38.0gr load had high enough pressure to unseat the primer immediately after the 42.8gr load really locked up my bolt. Unless I caused damage to the chamber and there is a crack pushing inwards tightening the chamber but I can't see that.

[TheBelly]

That engagement area rule won't exist in numbers relating to OAL, or at least it shouldn't. An OAL of 2.800 can have different amounts of engagement area based on trim length of brass. My trimmer trims from the neck. Therefore there'd be a different ratio of engagement area if a case is trimmed to 2.005 rather than the SAAMI spec of 2.015.

Here's a question: how would you measure (down to .001) the engagement area of a bullet that is loaded into a piece of brass? You can do it, but you'd have to use some arithmetic and critical thinking skills.

Yes, that's a challenge, and please show your work.