If you measure base to ogive and know where the bullet hits the rifling, you set the die up based on that length with some clearance and you’re done. You want some jump, but as long as never exceed the known jam length, it’s no problem.ReadyAimDuck wrote: ↑Fri Dec 25, 2020 11:24 pmFor me, this is the first gas gun I've really reloaded heavily for and I'm still at the point where I have a hard time trusting that the bullets will stay seated where they belong with only the neck tension. Part of that distrust is the amount of time it has taken me to understand what the OAL should be based on feeding. And feeding with different magazines, different weighted BCGs, Buffers, Gas Block settings, etc. In the journey to find fully functioning subsonic loads in the sub 165 grain range, I've run into everything under the sun that can go wrong and lead to bullets stuck in the chamber, squibs, etc. In fact, I've gotten into the habit of popping the rear take down pin, sliding the bolt carrier out, and looking down the barrel from the rear after each shot to make sure there is no obstruction anywhere, until I am completely confident in the load. A lot of this testing has been done from just outside the door at a huge hill without a target on it. This is because these loadings were intended to find loads in the light bullet weights that cycle the action, and not necessaryily to find good groupings, but to find those that remain subsonic. That, and theres just a whole heck of a lot of snow on the ground that I don't feel like trudging through to set the target up on. So, basically for now I'm just aiming at the giant hill and taking note of the sound, the cycling of the action, etc.
These are published loads and C.O.A.Ls that I am using, so it might sound like paranoia, but I've had more than my share of failure to feeds with the bullet being pushed way back into the case, or even stuck in the chamber when having to really pull hard on the charging handle after a FTF (in this case I pushed it in all the way with the forward assist, then thought better of that idea). Its taken a bit of trial and error and borrowing from other's who have posted their trial and error, to learn about the measurement of the ogive to base, and COAL, in a gas gun for this round. And along the way I've seen where that measurement can be slightly off and the rounds end up being pushed back into the case enough to make me nervous. So, I've been religious about crimping as a result, with the mindset that it could prevent a round from chambering that could be pushed back into the case too far and compressing the powder unsafely. Whether or not this makes a ton of sense, I cannot say for sure. I am not extremely well-versed in loading for gas guns. Most of my loading experience is with revolver cartridges and bolt guns.
Part of the problem is what you are trying to do, light subs, under 150 grains, in a gas gun. It’s just not practical. The powders that will cycle lighter bullets burn so poorly that after a few shots the action is so clogged with carbon and unburned powder, you have problems feeding and chambering.
Moving between longer and shorter seated depth of the bullet or changing bullets complicates that also because the garbage builds up in front of the bullet rapidly. So a longer bullet needs to try and seat in chamber full of crap. Once it’s forced in and even more so if you have to use the forward assist, it’s not coming back out.
The lighter the bullet the less crimp you need, it’s the speed of chambering, and the sudden stop that moves the bullet forward. The heavier the bullet the more likely it is to slip. A bit more or less crimp changes starting pressure, which effects powder burn rate and accuracy and can be used to fine tune a load. With that said, I never crimp.