Can crimp and OAL drastically effect accuracy in 9MM?

[MP-5]

Even after reloading for years, I guess we still have learning experiences. I was working up a load in 9mm for my Glock 17. I stumbled across a warm load after some trial and error and came up with a load that will consistently shoot 1" five shot groups @ 25 yards off of a bench. It is the most accurate pistol handload I've ever developed. (And proud of it!) The load is a 124 grain FMJ on top of 7.9 grains of Blue Dot, OAL is 1.150 and crimp is .376 with Federal primers and Rem cases. It shoots lights out! Ive also tried it out of my Beretta 92 and it still is OK to very good as far as accuracy (about the 2" mark) @ 25 yards for 5 shots.
Acquiring a used SIG 228, I stuffed this handload into it and proceeded to shoot 5"-6" groups @ 25 yards. Since then I've experimented with other powders, and powder charges but have kept bullets, OAL, crimp and primers the same (since changing too many variables would be pointless). Still, with two different loads with Blue Dot and three different loads with Bullseye powder, accuracy has not changed. (6" groups @ 25 yards) Frustrated, I thought it was the gun and sent it to SIG to see what they could figure out. Back came the pistol in a couple of weeks, with a test target with a very impressive group with factory ammo. Turning back to my reloads, they still shoot shotgun like patterns out of this weapon.
The other day I took two factory loads out and shot them out of the 228. The first was Winchester 147 grain subsonic and the second was Federal 124-grain +P+ Hydra-shock. The 228 put 4 of 5 subsonics into an inch with the last round opening it up to the 2" mark. Impressive. The Federal load had three rounds under an inch with the other two rounds side by side opening up the group to 2.5 inches @ 25 yards. Obviously the 228 like factory ammo.
I have been reloading 9mm for over ten years and never had accuracy problems like this. The Beretta and Glock seem to like a wide spectrum of loads. I know the OAL is a bit long in by handload but would that really affect accuracy out of my SIG? Are SIGs known for liking or disliking certain lengths or crimps?? Would a tighter crimp be better of worse for accuracy? I’m really puzzled with this SIG as my other 9mm never gave me any accuracy trouble like this. Sorry for the long winded post but I need some technical advice!!

 

[HSMITH]

Yes, crimp and OAL can drastically effect accuracy. Play with one at a time, and be careful not to overcrimp. Even just .005" in OAL can make a big difference.

 

[Jeeper]

definately watch overcrimping. I have found that crimping has never done anything for me but ruin accuracy. I just return the case to straight after expanding (or de-bell). Both things can affect accuracy but I would start with a looser crimp and as long of a load as will cycle in your mags.

One other thing that I would do is to let someone else shoot the gun. I dont mean this as an insult but there is always a possibility that it is you. This will remove that factor from the equation. Sometimes peoples hands and physical makeup can affect certain grips or triggers. I doubt it is you but ya never know.

 

[P95Carry]

If resize is good and adequate then neck tension should all but cope with bullet hold - just enough crimp to negate any previous flare.

OAL - now that to me is a mega factor. High pressure round is this and even a small reduction in OAL can have quite profound effects on pressures. I would certainly pay most attention to OAL - regarding any inconsistencies and of course, crimp MUST be enough to avoid any changes in such.

One other factor - the freebore of a given barrel will sometimes affect accuracy with a given OAL - and I have noticed a considerable difference in OAL BTW within factory offerings!!