.40 cal OAL variations. Why?

[blueline541]

I'm loading on a Dillon 550, Lee dies w/FCD, mixed brass, 165 grain fmj. For whatever reason I've recently been getting a variety of lengths on my finished rounds. I'm shooting for 1.125 and I'm getting everything from 1.123 to 1.128 with most falling around the target length but not hitting it. With .45 and 9mm I'm usually dead on, but now that no longer happens with .40.

These are just plinking rounds and it's no big deal, but I'd like some kind of idea why this is now happening.

[creophus]

What heastamp(s) is on your brass?

[blueline541]

A little bit of everything. Reckon that could be the culprit?

[creophus]

Don't know, but that would be where I'd start. Do you get consistent OAL when using the same headstamp? If so, then sort for the headstamp or just deal with the inconsistency.

Might be something else though.

ETA: Avoid AMERC brass like the plague.

[blueline541]

The only decapping pin I ever broke was on a piece of AMERC. I hate that stuff and have banned it from my range.

[creophus]

Good man. I had an OAL problem and could figure what was wrong with the round upon looking at it.

I flipped it over and boom, "AMERC". I held the round between my thumb and index finger and pushed the bullet further into the case a noticeable distance.

Right then and there I culled out all the AMERC that crept into my brass stash.

[fredj338]

Are you seating w/ cases in all stations? It matters for repeatability. Also make sure the shell plate is as tight as possible & still turns. You'll get some "spungyness" that can cause variation. Really though, the bullet nose shape can vary enough to give you a 0.002" diff. It isn't going to affect your load.

[Tailgunner]

Ummm, your holding OAL within .005, and your worried about it??????????????????
That's less than the (actual) thickness of a dark hair.

Let me put it another way, do you get freaked out if while your speedometer reads 55, your actual speed may vary between 54.9 and 55.1 ?

[JW6108]

Measure some .40 cases sometimes.....all over the map and almost always well below recommended trim-to length.:confused:

But, no problems. Thanx, Glock.

[AdamN]

Case length shouldnt matter to your OAL, but like TG said I sure wouldnt worry about .005.

More than likely its the difference from where the bullet seating die contacts the bullet and the fact that you measure to the nose of the bullet.
There will be a little variance between the ogive where the die lands and the nose of the bullet where you measure.

[MakeMineaP99]

When we talked about this, Blueline, I was under the impression your OAL variance was 50 thousandths or .050", not .005".

5 thousandths is within the tolerance stack up of the press, meaning the clearance between the toolhead and press, shell plate and subplate and so forth.

Don't worry about it.

[blueline541]

When we talked about this, Blueline, I was under the impression your OAL variance was 50 thousandths or .050", not .005".

5 thousandths is within the tolerance stack up of the press, meaning the clearance between the toolhead and press, shell plate and subplate and so forth.

Don't worry about it.


That was the case with the RCBS dies. I still haven't figured out what was going on with them. Hence the swap to Lee, although the .45s and 9mm dies are almost dead on.

[MakeMineaP99]

It could be a sign to give up 40. ;)

Regarding the RCBS dies, the only thing I can think of is the dies themselves are the problem. I believe a phone call to the folks at RCBS might be worth the time. You may have worn those out. It's the only variable I keep coming back too as the problem.

[Oreo]

I noticed the same problems with OAL variance when I started reloading. My variance was +- .01" roughly. But that was with Winchester FMJ's. When I started loading up some GDHP's I found the OAL variance tightened up a bunch. The same lee dies & hornady press used for both. So, I have to assume the bullet plays a role one way or another.

[MCK45ACP]

Just for kicks. Back off your crimping die and run a batch. Say 30 rounds. Hand eject them (don't let them fall into the bin) then check the OAL.

[BigSlick]

A very real possibility is a slight difference from one bullet to the next. Measure a few bullets, it can be suprising.

Otherwise like the others say .005 ain't anything ta lose any sleep over unless you're on da bleedin edge, in which case if the .005 makes a difference you prolly need ta back it down a lil bit anyway

[Steve Koski]

It could also be due to loading with a "full deck" on the 550 and not. When the deck is full, the COL is a titch longer than rounds loaded one at a time. .003 to .005 difference I believe.

[mbradst]

DO you have another seating stem you could try? Maybe the stem holds the bullet funny or something.

[creophus]

Blueline, have you fired these rounds yet?

[BigDog[RE]]

Try cleaning out your seating die, sometimes you get a build up of gunk in there.