Chuck R.
Member
As per this thread:
I've been playing with creating a false shoulder when 1st time sizing belted magnum brass IOT minimize case stretching from the web area. This started with a new Bartlein barrel on my 700 and some seriously undersized new FC brass (made to headspace on the belt VS shoulder as per normal specs).
The intent was to use the false shoulder to keep the case head against the bolt (same effect as jamming a bullet) and get the brass to form without the normal stretching at the web. Extra time involved is about 10 minutes per 50 rds. Idea came from here:
Another issue was even with the 1st firing, the brass hadn't expanded enough to have any resistance when closing a stripped bolt. So IF a did the standard; measure, subtract .002-3" to set up my sizing die, I'm still "short" and headspacing on the belt .
The steps I used:
1. Run the .32 neck expander into brass
2. Run a .338 neck expander into brass (.32 wasn't enough of a false neck and I lost 2 pieces of brass going right to .33)
3. Neck size to achieve a "crush fit" on the false shoulder created in step 2. I used my die set up for FL sizing and backed it off using a 0.0245" die shim.
4. Load. I used a bunch of Midway 168 OTM "2nds" that I bought for practice.
I've been shooting this as practice loads while fire-forming, it's a full power load; 168 grn at 3179FPS, accuracy has been running just under MOA consistently, easily stays on my swinger at 547 yds. The load mimics my Nosler ABLR 168 grn load.
Some measurements (20 cases each method, Hornady comparator, caliper NOT set to "0"):
AVG Measurement for new brass was 4.264"
AVG measurement for once fired brass (without false shoulder) is 4.284", SD was 0.009 (.020" expansion!!)
AVG measurement for once fired brass (with false shoulder) is 4.286", SD was 0.008 Gained .002"
The good news is, with the false shouldered brass out of 50 rds I had 5 that formed enough to offer resistance while chambering. The non-false shouldered brass chambered with zero resistance for all 50rds, bolt just dropped.
So for this next loading at least I've set my "bump" to 4.286" and will track through the next loading.
So, does it work?
I dunno.. yet.
Using my RCBS "pick" I'm not feeling much of a difference in the web area. Teslong Bore scope showed the same. I am happy about the extra .002" in case expansion on the initial firing. I now have 50rds of normal sized and 100rds of the initial fire forming using the false shoulder. I'll continue to track firings, and expansion for both lots and see what happens after multiple firings.
Belted Magnum Brass Prep: False Shoulder?
Working with my newly re-barreled 300WM and I'm getting 0.020" average headspace expansion on new FED brass using a Hornady comparator and taking 10rd samples. New brass just had the necks sized, no shoulder bump. AVG Measurement for new brass was 4.264" AVG measurement for once fired is...
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I've been playing with creating a false shoulder when 1st time sizing belted magnum brass IOT minimize case stretching from the web area. This started with a new Bartlein barrel on my 700 and some seriously undersized new FC brass (made to headspace on the belt VS shoulder as per normal specs).
The intent was to use the false shoulder to keep the case head against the bolt (same effect as jamming a bullet) and get the brass to form without the normal stretching at the web. Extra time involved is about 10 minutes per 50 rds. Idea came from here:
Another issue was even with the 1st firing, the brass hadn't expanded enough to have any resistance when closing a stripped bolt. So IF a did the standard; measure, subtract .002-3" to set up my sizing die, I'm still "short" and headspacing on the belt .
The steps I used:
1. Run the .32 neck expander into brass
2. Run a .338 neck expander into brass (.32 wasn't enough of a false neck and I lost 2 pieces of brass going right to .33)
3. Neck size to achieve a "crush fit" on the false shoulder created in step 2. I used my die set up for FL sizing and backed it off using a 0.0245" die shim.
4. Load. I used a bunch of Midway 168 OTM "2nds" that I bought for practice.
I've been shooting this as practice loads while fire-forming, it's a full power load; 168 grn at 3179FPS, accuracy has been running just under MOA consistently, easily stays on my swinger at 547 yds. The load mimics my Nosler ABLR 168 grn load.
Some measurements (20 cases each method, Hornady comparator, caliper NOT set to "0"):
AVG Measurement for new brass was 4.264"
AVG measurement for once fired brass (without false shoulder) is 4.284", SD was 0.009 (.020" expansion!!)
AVG measurement for once fired brass (with false shoulder) is 4.286", SD was 0.008 Gained .002"
The good news is, with the false shouldered brass out of 50 rds I had 5 that formed enough to offer resistance while chambering. The non-false shouldered brass chambered with zero resistance for all 50rds, bolt just dropped.
So for this next loading at least I've set my "bump" to 4.286" and will track through the next loading.
So, does it work?
I dunno.. yet.
Using my RCBS "pick" I'm not feeling much of a difference in the web area. Teslong Bore scope showed the same. I am happy about the extra .002" in case expansion on the initial firing. I now have 50rds of normal sized and 100rds of the initial fire forming using the false shoulder. I'll continue to track firings, and expansion for both lots and see what happens after multiple firings.