Chamber length and brass, to trim or not to trim, that is the question.

[earl1704]

Given; 300 Win Mag, factory rifle, no modifications.
Reload; Nosler brass, Hornady 110gr V-Max, H 4350, 76.8 gr. Federal 215 primer
Primer pockets uniformed, flash hole deburred, annealed every 2 shots, full length
resizing, chamfer inside and out of necks, before loading I use an expander
die to uniform necks and use a brush in drill to 'clean' inside of the necks.
I do NOT sort brass by weight.

Measured chamber length is 2.6495 (Sinclair chamber plug)
Brass fired upwards of 5 or 6 times (or more).
Longest brass 2.6445
Shortest brass 2.6240
Book trim to, 2.610

I general do not trim brass thinking it will grow to near my chamber length, where
I would trim back about 3k for uniformity. However my brass is so un-uniform in length I must
(I think) trim to something else, its just not going to get there. The question is what length for max accuracy? Do I just take a guess? Is there a rule? I cant send 100's of rounds to test every length with the cost and availability of
components being the problem it is at this time.
I have found when my brass does get to the 2.64XX area the necks tend to split.
This will be a wolf hunting round, currently shoots well to 500 yds., 1 MOA, but I do get fliers.
SD 39.3 (need to do much better)
Low 3632 fps
High 3741 fps
Extreme spread 109 fps

Do I need to rethink brass, load or anything else to get the SD down?
Any other thoughts? Trying to find a better way of thinking or looking at this.

Thanks ...........Earl

 

[MagnumManiac]

In my rifles, I trim to be within .010" of CHAMBER LENGTH, and keep it there more or less.
If you notice that your brass grows, during sizing, more than .010", even if it's only ONE piece, then I suggest you keep your brass to .020" under chamber length.

Cheers.

 

[Mikecr]

I like your general plan.
Don't trim until they're at least in the same zip code of chamber end. If they'll never reach it, then never trim.
Being way too short is worse than having normal length variances.

 

[Alex Wheeler]

Some of the best shooters I know intentionally trim much shorter than chamber length. The guns shoot better. Less fliers. When that case is under pressure it squeezes longer. I prefer to be at least .020" short of the chamber, .030-.040 doesnt bother me a bit. .010" does.

 

[Hugnot]

There must be a reason why variable & excessive stretching is happening. I have a .300 WM & F/L size on the shoulder and trim .020 or more and can go 3 or more firings before trimming again. F/L sizing & head-spacing using the belt might increase non-uniform case stretching by blowing the brass forward. I have found that excessively long cases tend to show heavy powder residue along the sides of the necks & brass body with deposits on the bolt face and front part of the bolt. My guess is that the crimping action resulting in jamming a round into the front of the chamber prevents neck expansion. Fired & smudged cases show abnormally small neck diameters.

I have shot some rodents with my .300 WM: the load being H4350 & the 150 Hornady SST's. Excessive recoil & blast made me quit.