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>> To Trim Or Not To Trim? :: By DOK on 2001-07-20
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Several weeks ago, Southpaw expressed concern about his new Starline .454 brass. His new brass was both shorter than spec. and the length varied .005”. I ordered 250 .454 Starline brass to validate Southpaw’s results. And my results matched his, short and length varied .005”, thus trimming will be required.

I then sampled my Starline .44mag brass and found the same discrepancy, short length and also varied .005”. Rather embarrassed to admit that due to Starline’s excellent quality reputation, I had not worried about length/variation and had not been measuring the new Starline brass. So now it appears I’ll need to trim that brass also – or will I? What is the effect of not trimming brass that varies .005” and/or may not have a square mouth? The following tests address the impact of not trimming the Starline .44mag brass.

I used a .44mag Super Blackhawk, 7 ½” barrel with 2X7 Burris scope on a T’SOB mount for the test. All testing was done from bench rest at 25 yd. distance and the Chrony was set 10 feet from muzzle. All test included 50 rounds untrimmed brass and 50 rounds trimmed brass (trimmed to 1.274” after sizing). Three rounds of 50 each (trimmed and untrimmed) were fired, with the trimmed brass being trimmed after each firing. The bullets were 275gr. gas checked lead, primers were CCI 350 and powder was 20.2grs. of 2400. This is the max. load for 275gr. bullets per Lyman recommendations. I should mention that the bullets were seated so the top of the brass was parallel to the top of the bullet crimping channel. Thus any brass lengthening could impact the bullet. Examining the loaded rounds after the 2nd and 3rd loading under a 3X lighted magnifying glass, you could see that in fact, the brass did press on the bullet at the top of the crimping channel.

Specification length for the .44mag is 1.280”. The new Starline brass averaged 1.2728” before sizing and 1.2754” after initial sizing. The variation (ES) before sizing was .005” and .005” after sizing. The data for 50 untrimmed brass is as follows:
Length
New
Initial sized
2nd sized 3rd sized 4th sized
1.273" 1.275" 1.277" 1.278" 1.279"
Extreme Spread
.005 .006 .005 .005 .005
Std. Dev.
.888 1.127 1.133 1.010 1.380

As before, 50 rounds of each trimmed and untrimmed were fired three separate times to conduct the accuracy and velocity tests. This represented ten 5-shot groups each on three separate days for a total of thirty 5-shot groups for both sets of brass. The results are as follows:

Five Shot Group

Accuracy
1 Rd.
2 Rd.
3 Rd. Avg.
Untrimmed
1.80 1.67 1.66 1.71
Trimmed
1.82 1.66 1.53 1.67
Extreme Spread
1 Rd. 2 Rd. 3 Rd. Avg.
Untrimmed
2.39 1.12 1.93 1.51
Trimmed
1.24 1.11 .34 .90

Conclusion: I will not worry about trimming the brass. I either discard brass after 3 rounds of full loads or downgrade it to plinking rounds. The only performance data that appeared significant to me was the variation (see ES data) between the 5-shot groups for untrimmed brass. If you want consistency, the ES for trimmed brass is .61” better on average than the untrimmed.

Since most of my shooting is off hand and no money changes hands, the improved accuracy average of .04” for trimmed brass doesn’t appear to be worth the effort.

But I’ll also predict that those of you that trim your brass will continue to, and those that don’t trim will now have an excuse.


Dan


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