Crimping Rifle Rounds

[Cfshooter]

Yep, here we go, talking about crimping rifle rounds, but rounds getting slammed home by a bolt carrier group in a gas gun. I did a little test and on bullets seated long (much longer than mag length), each case .002 neck tension (mandrel). I noticed set back (and forward ) after round was chambered by bolt slamming it home. It typically took 3 rides home before the bullet settled at its resting spot. I did the same test on bullets seated deeper than that “resting” spot, and I did not notice any setback. I then took it to the range and shot 5 shot groups, 2 groups each (long crimped, long not crimped), a group at “resting” spot, and also a longer crimped depth. The group sizes for the long not crimped was noticeably larger (about 1/3 moa) than the other two, and the ES almost doubled. The long crimped and “resting spot” not crimped had almost identical groups and chrono numbers.

Just figured I would share my findings.
YMMV

 

[jepp2]

d a little test and on bullets seated long (much longer than mag length), each case .002 neck tension (mandrel). I noticed set back (and forward ) after round was chambered by bolt slamming it home

For the rounds loaded longer than magazine length, what was your process for chambering them?

 

[Cfshooter]

For the rounds loaded longer than magazine length, what was your process for chambering them?

I hand fed each round like I would during a relay in a match. I started the round into the chamber about half way (until it was straight) and then sent bolt home.

 

[markm87]

I've done a few crimp tests in .223. First time the lack of crimp hurt my groups by 3/4". I did another a few months back and there was no significant difference.

A lot of this depends on the total load process. I.E. I don't anneal 223, so crimp helps (I think) to even out neck tensions.

I don't crimp 308 or 6.5cm gas gun ammo however.

 

[Cfshooter]

I've done a few crimp tests in .223. First time the lack of crimp hurt my groups by 3/4". I did another a few months back and there was no significant difference.

A lot of this depends on the total load process. I.E. I don't anneal 223, so crimp helps (I think) to even out neck tensions.

I don't crimp 308 or 6.5cm gas gun ammo however.

What I noticed is that if all of the neck area of brass was in contact with the bullet bearing surface, there was no setback when chambering. It was only on the long seated ones.

 

[williepete]

How far out were you shooting

 

[Cfshooter]

How far out were you shooting

test was done at 100 yards, that is all I really needed to see if there was any difference.

 

[Intheshop]

Roll crimp as produced with a typical seater die? Or something else?

 

[Cfshooter]

Roll crimp as produced with a typical seater die? Or something else?

Lee Factory Crimp Die was used. I did not squeeze them very hard, just enough to feel it was actually doing something.

 

[Richard Jones]

Interesting. I normally don't crimp rifle stuff, but 300 Blackout and 223 for the ARs get a pretty good crimp, due to all the differences in neck thicknesses of the brass I use.

Was this all the same brand of brass? Same neck thickness (within reason)?

 

[Doug Casner]

I always thought it might give you a more consistent powder burn. Makes mine feed better. Doug

 

[762plinker]

maybe START WITH A TEST ON HOW MUCH NECK TENSION IS REQUIRED TO HOLD THE BULLET BEFORE IT MOVES....THEN THE REST AINT NECESSARY.

 

[Cfshooter]

Interesting. I normally don't crimp rifle stuff, but 300 Blackout and 223 for the ARs get a pretty good crimp, due to all the differences in neck thicknesses of the brass I use.

Was this all the same brand of brass? Same neck thickness (within reason)?

All the same brass (Starline 556, 2nd firing).

 

[Cfshooter]

maybe START WITH A TEST ON HOW MUCH NECK TENSION IS REQUIRED TO HOLD THE BULLET BEFORE IT MOVES....THEN THE REST AINT NECESSARY.

that would work too, but not what I was testing at this time.

 

[762plinker]

that would work too, but not what I was testing at this time.

the point was you tested out of order,,,fix the real problem

 

[jepp2]

I started the round into the chamber about half way (until it was straight) and then sent bolt home.

I'm sure you know this, but loading that way puts much more bolt speed, thus inertia on the round as it suddenly stops during chambering. The bolt is designed to scrub off some of the energy as it strips a round from the magazine and the round strikes the feed ramp of the barrel extension. I also makes it slightly more prone to a slam fire.

If you window your magazine, you can easily add 0.100" COAL and still feed from the magazine. I only cut a window large enough to allow me to load 5 rounds in a 10 round magazine.

 

[Intheshop]

Is that a Lee collet crimp die?

I've used those..... a crimp is like a crutch,sometimes exactly what the load needs. It's very similar to a jam in how the ignition "seems" to be hotter/cleaner?

Also use a gentle crimp on hunting loads going in/out of battery repeatedly.... dropping and mishandling.

 

[Cfshooter]

I'm sure you know this, but loading that way puts much more bolt speed, thus inertia on the round as it suddenly stops during chambering. The bolt is designed to scrub off some of the energy as it strips a round from the magazine and the round strikes the feed ramp of the barrel extension. I also makes it slightly more prone to a slam fire.

If you window your magazine, you can easily add 0.100" COAL and still feed from the magazine. I only cut a window large enough to allow me to load 5 rounds in a 10 round magazine.

View attachment 1398115

Did you cut that with a pocket knife? lol, I'm kidding, I like it! But, I use these long loads for F-class matches and not allowed to mag feed.

 

[Cfshooter]

Is that a Lee collet crimp die?

I've used those..... a crimp is like a crutch,sometimes exactly what the load needs. It's very similar to a jam in how the ignition "seems" to be hotter/cleaner?

Also use a gentle crimp on hunting loads going in/out of battery repeatedly.... dropping and mishandling.

Yes sir, I just put a very light squeeze on them with it.

 

[jepp2]

Did you cut that with a pocket knife?

Even worse, someone turned me loose with a ziz wheel on a dremel. Looks like a 100% Bubba job, but it worked so well, I never tried to make another one done properly.