Anthony.L;1811577]My $.02 as someone who hand loads .308WIN and .338LM for match grade ammo in my bolt-guns.
Always crimp. Crimping increases accuracy as the case mouth pressure on the projectile is the same from round to round. Over crimping can cause issues, so understand the correct use of crimping.
Anthony.L,
I have to respectfully take issue with the above statement. Important to note that I do not want to start any war or pissing contest. I will however strongly disagree with your opinion on crimping.
It is important to note that I do not engage in unfounded suppositions - my data, processes and opinion is grounded in decades as a professional - as a shooter, gunsmith, ammunition developer and professional (read paid) competitor.
With that said - and dealing specifically with match grade bullets - as the OP first brought to the table:
1. Crimping does NOT increase accuracy.
2. Crimping does not contribute to developing the same case mouth pressure.
Crimping has absolutely zero place on a match grade bullet.
If you crimp a case neck onto a match grade bullet - you are without question distorting the bullet. This is not opinion - it is fact. A crimp mechanically displaces the jacket which in turn displaces the lead core. That core MUST move somewhere - it is going in one of two directions - front or back. If it moves rearward, then the result will be a distorted base or boattail. It it moves forward, it will fill some of the void near the meplat (tip/hollowpoint area). This will impact the CG and you'll get a nose heavy bullet that will exhibit all sorts of gyroscopic permutations - i.e. potentially severe precession. Additionally, when shooting bullets that are made with high end jackets - i.e. J4's - these thin jackets can experience jacket separation from the core - usually evidenced by small grey puffs of smoke about 20ft from the muzzle...that's the bullet coming apart in flight.
Almost 10 years ago I had a long conversation with Walt Berger. He knows a bit about bullet design. I was in the midst of developing long range 556 ammo (1000yds stuff) using his 90gr VLD bullet. VLD's are finicky and sensitive to all sorts of external influences. The discussion centered around designing the throat / free bore / lead angle in the chamber to take full advantage of this bullet - which is very long. My initial direction was to find a length where I had nearly zero free space in the case (100% load density) I knew basically what the charge weights were going to be - fairly narrow window. So, the intent was to put the base of the bullet right above the powder column. He ran some calculations and came back to me with; "That won't work, you destroy the accuracy of the bullet." He went on to explain that pushing a bullet too far down inside the case, powder column will actually collapse the boat tail when the cartridge is fired. Once ANY distortion of the base occures - accuracy is gone. This small detail changed the entire approach - I went with a slower powder / increased the load density back up to take up the space in the case along with the obviously longer length. (BTW - a LR 90gr VLD 556 is about 2.520" long) The point of this story is that during our conversations - I sarcasticlly said to him that I guess I won't crimp the bullets either. He didn't think that was funny. This lead into a discussion on crimping. There is a need for it in certain pistol ammo, lead bullets (especially with lube) heavy recoiling large caliber hunting bullets and military ammo that is used in semi-auto / full-auto weapons. A crimp is used to prevent setback under recoil when the cartidges are in a magazine or belt. As far using a crimp on a match grade bullet... utter blasphemy. DO NOT DO IT.
As further evidence - consider the US GI match grade ammo program. I would submit that the engineers at Frankford Arsenal, LC and countelss other ballistic labs considered crimping - in every single instance and type - the bullets are NOT crimped.
M-72 Cal .30 w/ 173gr FMJBT - no crimp
XM-118 Experimantal w/ 173gr FMJBT - no crimp
M-118 National Match w/ 173gr FMJBT - no crimp
M-118 Special Ball w/ 173gr FMJBT - no crimp
M-852 Match w/ 168gr HPBT - no crimp
M-118 Long Range w/ 175gr HPBT - no crimp
Mk 316 Mod 0 w/ 175gr HPBT - no crimp
M262 Mod 0 w/ 77gr HPBT - no crimp
None of the Federal Gold Medal match has a crimp, none and we shot the 69gr stuff out of the box at 200 & 300 yds - it would shoot high high x count cleans. Same same with the 77gr loads. None had / has a canelure or crimp.
The only exceptions are the Mk262 Mod 1 which has a FAINT canelure in the bullet from the mfr and the 556 Optimized w/ 70gr TSX - BOTH designed BTW as COMBAT loads - they are accurate due to the quality of the bullet, but they are not type classified as precision/match grade ammunition. (additionally the 70gr TSX is a solid copper bullet - no core)
The only "treatment" on the necks of all that GI match ammo is/was an asphalt sealant - which by the way was found to increase accuracy when the seal was actually broken. We would run all the ammo through a bullet puller to slightly pull the bullet by an 1/8", then reseat to proper length.
Every one of those match loadings was run through gas guns & mag fed weapons.
So - bottom line after all my hot air. If the bullet does not have a canelure - DO NOT CRIMP IT.
If you want to gain consistency (there's that word again 
) in a neck area process, then expanding on a precision mandrel will help (gets the necks perfectly round) then turn the neck to achieve the exact same wall thickness for a full 360 deg. then run the brass through a bushing neck sizer - you will gain astoundingly consistent neck tension which WILL impove acuracy. If you want to go full psychotic, then get into neck annealing and get a hardness gauge..
Hope this helps, and again, nothing personal Anthony, just trying to offer hard data to refute all the internet drizzle and poop.
Last edited by opsoff1; 12-12-13 at 13:49.
opsoff
"I'd rather go down the river with seven studs than with a hundred shitheads"- Colonel Charlie Beckwith
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