legaleagle
04-02-2017, 21:58
Been having major issues with SA micro compact. Bought new and have yet to get 3 rounds in a row after 350 rounds to cycle without ftf. No fate issues at all. Major headache. Have researched issues like crazy for months. Polished ramp on barrel and frame, switched mags, switched ammo, buffed chamber, reworked extractor, added throat to barrel as had none, checked for 1/32 gap from frame ramp to barrel ramp. Still got ftf with 230 fmj where top of bullet was touching top of chamber, case at base of bullet where seated was touching throat and back of the rim was touching the slide - 3 points of contact. There was no extractor engagement as the rim was not touching it. No matter of force would send slide into battery. However, if you touched the front of barrel with a couple pounds of force by tapping with a dowel the ftf loaded and went into battery. WTF. I believe I have figured the issue out.
You could add heavier recoil spring spring but this does not solve problem and when it's gets weak the ftf will return. You could add extreme throating beyond the 35 degree and .020 to .030, but you risk leaving the case unsupported too much. Some throat is needed because of the extreme angles in the short strokers, but nothing more than the government or commander. You will likely be ok with about half. If you do this be sure to polish it and the ramp. Remember a little resistance loading similar to 3 point ftf is normal to slow the slide down. You will see a small horizontal mark on brass when it is right.
The big issue and often overlooked or blamed on mags and extractors is the radius of the barrel arch on the link and slide stop pin. Here's where it gets technical. The link pin can be too long by .002 and cause this ftf. This is called riding the link. When the barrel starts to move forward it also moves upward. If the link is too long it is like a pole vaulter without enough speed and the recoil spring and slide cannot overcome the 3 points of contact. Also as the barrel moves up the angle of entry for the round gets steeper and thus when steep enough the round jams into 3 point jam and no amount of force will overcome it. This means the radius is too long as it starts too soon and rises too fast. The proper length involves measuring the height of the barrel lugs to where the slide stop pin is supposed to ride against the barrel. Typically the link pin is about .278 center to center from the center of the barrel lug hole to the center of the slide stop pin. You can measure each hole - the barrel link hole and the slide stop pin frame hole and divide by two, then measure from the barrel hole bottom to the bottom of the lugs - this should give you the link length needed. Assuming your barrel lockup is not out of speck you can take the slide stop pin and insert it in the link with barrel removed so that it is the lock backed position (too short of a link will lead to unlocking faster and having too much pressure in case is a problem for gun and you - STOP here if you do not understand the mechanism so you do not hurt yourself with a kaboom). The slide stop pin should rest on the barrel lug and not teeter totter on the link. Be sure the the pin is on the bottom of the lugs and not against the back of the lugs. Here if the pin teeter totters the barrel will ride the link and not the pin. In the SA micro compact there was a ridge of metal inside the link that caused the link to ride on pin. This induced early rise time in the barrel making the entry too steep for the round and whalla the ftf. After a few strokes of the file and keeping the profile of the pin in the link hole for the pin, and testing the pin repeatedly, the pin finally rested on the barrel lug and not the pin. Be sure to keep the hole perpendicular to the sides or you could get an imbalance and create a sideways wedging and jam. Effectively shortening the link this allows the barrel to remain down on the frame bed slightly longer as it should and the round to enter and come over the throat threshold more. It keeps the entry angle shallower and feeding is now proper or more so. If you still have problems the dimensions on the link and barrel lugs may be more out of spec than this can correct. This is also more sensitive the shorter the barrel.
After figuring this out the rounds cycled smoother and without issue from 5 different brands of mags. The only noticeable stutter are those mags with a dimple to hold the last round in the mag. This is a proper mag design. Even riding the slide a little did not recreate the problem whereas it was repeatable with every round and riding the slide. Obviously live fire testing will reveal success or not.
I hope this helps others to understand that ftf is not always about extractor tension or mags and release points on the lips. Obviously on the short strokers earlier release of the round from the mag is critical to begin reducing entry angles asap, but not too soon.
Note: as to Wilson mags they do not have dimple and work fine. Also I noticed the follower tends to ride a bit higher than flat metal follower mags which may also assist in reducing the entry angle. This is noticeable only on the last round in the mag.
You could add heavier recoil spring spring but this does not solve problem and when it's gets weak the ftf will return. You could add extreme throating beyond the 35 degree and .020 to .030, but you risk leaving the case unsupported too much. Some throat is needed because of the extreme angles in the short strokers, but nothing more than the government or commander. You will likely be ok with about half. If you do this be sure to polish it and the ramp. Remember a little resistance loading similar to 3 point ftf is normal to slow the slide down. You will see a small horizontal mark on brass when it is right.
The big issue and often overlooked or blamed on mags and extractors is the radius of the barrel arch on the link and slide stop pin. Here's where it gets technical. The link pin can be too long by .002 and cause this ftf. This is called riding the link. When the barrel starts to move forward it also moves upward. If the link is too long it is like a pole vaulter without enough speed and the recoil spring and slide cannot overcome the 3 points of contact. Also as the barrel moves up the angle of entry for the round gets steeper and thus when steep enough the round jams into 3 point jam and no amount of force will overcome it. This means the radius is too long as it starts too soon and rises too fast. The proper length involves measuring the height of the barrel lugs to where the slide stop pin is supposed to ride against the barrel. Typically the link pin is about .278 center to center from the center of the barrel lug hole to the center of the slide stop pin. You can measure each hole - the barrel link hole and the slide stop pin frame hole and divide by two, then measure from the barrel hole bottom to the bottom of the lugs - this should give you the link length needed. Assuming your barrel lockup is not out of speck you can take the slide stop pin and insert it in the link with barrel removed so that it is the lock backed position (too short of a link will lead to unlocking faster and having too much pressure in case is a problem for gun and you - STOP here if you do not understand the mechanism so you do not hurt yourself with a kaboom). The slide stop pin should rest on the barrel lug and not teeter totter on the link. Be sure the the pin is on the bottom of the lugs and not against the back of the lugs. Here if the pin teeter totters the barrel will ride the link and not the pin. In the SA micro compact there was a ridge of metal inside the link that caused the link to ride on pin. This induced early rise time in the barrel making the entry too steep for the round and whalla the ftf. After a few strokes of the file and keeping the profile of the pin in the link hole for the pin, and testing the pin repeatedly, the pin finally rested on the barrel lug and not the pin. Be sure to keep the hole perpendicular to the sides or you could get an imbalance and create a sideways wedging and jam. Effectively shortening the link this allows the barrel to remain down on the frame bed slightly longer as it should and the round to enter and come over the throat threshold more. It keeps the entry angle shallower and feeding is now proper or more so. If you still have problems the dimensions on the link and barrel lugs may be more out of spec than this can correct. This is also more sensitive the shorter the barrel.
After figuring this out the rounds cycled smoother and without issue from 5 different brands of mags. The only noticeable stutter are those mags with a dimple to hold the last round in the mag. This is a proper mag design. Even riding the slide a little did not recreate the problem whereas it was repeatable with every round and riding the slide. Obviously live fire testing will reveal success or not.
I hope this helps others to understand that ftf is not always about extractor tension or mags and release points on the lips. Obviously on the short strokers earlier release of the round from the mag is critical to begin reducing entry angles asap, but not too soon.
Note: as to Wilson mags they do not have dimple and work fine. Also I noticed the follower tends to ride a bit higher than flat metal follower mags which may also assist in reducing the entry angle. This is noticeable only on the last round in the mag.