Crimping 300ACC reloads

Rattling around in a 30 round mag isn’t going to change to OAL unless something severe happens. The Setback occurs during chambering.

I use a lee factory crimp die setup to just barely crimp the round to make sure the cartridge is loaded within spec.

Jackiesman said:

When I fired the 1st of the midrange rounds I checked the next 5 LOA for movement, and continued the process until all 6 were fired. I found some evidence of bullet creep (.001 to .005/6), and it has me wondering if I should put a mild crimp on the rounds.

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Measuring Length OverAll might not be the best way to see if the bullet is moving in the case.

First, tip to base, is not always consistent from one bullet to another. Like these SMK’s, for example.



So measuring Length OverAll with these to will show a .005” difference, despite the two being seated to the exact same depth.

You could also very easily distort the tip on soft point bullets so a way to measure from some point on the ogive would likely be more enlightening.

They sell tools that amount to a hole that becomes your “datum” or reference diameter. This one has 6 different diameters to choose from.



You can also get them where they attach to the blade on a caliper. A bit easier to use if your all thumbs.



Or you could just remove the seating stem from your die and use it.



Those methods would at least let you know if they are moving vs having different lengths to start with or are being distorted only at the tip.

FWIW, I don’t crimp my 300 blk at all.

Probably not much help here but I don’t crimp my .300 BO loads as I only load subsonic rounds for my SBR. The 190 Sub X doesn’t have a cannelure anyway

Jackiesman said:

Guess I’m leaving holes in my question. I'm aware that each bullet (especially PSP's and SP's) may vary considerably in length, which is why (when I'm test rounds) I measure, number and record the case length and OAL for each round. If if the bullet moves during clambering it would have a longer OAL, but I wouldn't know it unless I removed it from the chamber. But I'm measuring each round in the mag after each shot, and the OAL is getting shorter.

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I understand what you are saying and think it is me that isn’t relaying the information properly.

If you take a bullet out of the package, it should be in pretty good shape. Like the one on the right below. Have the tip contact anything during chambering, recoil and ejection for the subsequent measurement and it can be damaged, like the one on the left. Even if the bullet did not move in the case the OAL measurement will be different but ogive to base will be the same.



This is why I was suggesting ogive to base measurements, it removes tip distortion as a factor in your measurement.

I crimp my 300BLK. But then, I have LCD's for most all calibers and lightly crimp everything. I don't want to even think about setback and I'd like the crimp to be consistent.

Jackiesman said:

Wondering if anyone has experience in crimping 300ACC reloads. I always load near the minimum powder range, and recently loaded some 150 grain PSP rounds, and after firing kept increasing my loads up to mid range. When I fired the 1st of the midrange rounds I checked the next 5 LOA for movement, and continued the process until all 6 were fired. I found some evidence of bullet creep (.001 to .005/6), and it has me wondering if I should put a mild crimp on the rounds. I should add that the velocity over the crony was consistent, and like the lighter loads no abnormal slgns of pressure, I used LC brass at 1.365 with CCI SRP's at 2.200. Any insight would be appreciated.

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This is really dependent on what you're using for brass? If you've converted your own, and it's not been annealed, the spring back is going to cause you to have reduced neck tension. 300 AAC shouldn't need a crimp, if you've got bullet movement, first place to look is neck tension, which is a pretty common problem as a lot of people don't anneal converted brass.

Jackiesman said:

The saga continues: I tried to load some 110 grain round nose soft point for plinking, just fun shooting. Can't get them to feed from the mag, the point gets caught on the mag lip. Anyone have a hint? I considered trying to modify one of my mags, but before I try that I thought I would query to group.

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Some magazines, especially polymer, don't have the front relieved enough for reliable feeding of rounds in 300 BO. So far, I have found D&H mags to be good for 300 BO.

D&H on the left, and Del-Ton on the right.

I load heavy, powder coated lead bullets (subsonic) for 300 Blk. I had a learning curve, where I was having feeding issues. Virtually of it was solved when I switched from standard aluminum and pmags to 300 Blk-Specific Lancers.