Taper Bumping

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  • Last Post 4 days ago
OU812 posted this 2 weeks ago

Experimenting more with taper bumping. I used a PTG 310 diameter .75 degree per side reamer to cut both the  PTG die body and throat of my 308 Winchester short chambered 1-10 twist Shilen barrel.

Throat was cut deep to seat bullets long into throat. Gun shoots more consistently accurate now, but recoil is bad because of light weight rifle. Now I know why you need a heavy rifle to shoot more accurately on the bench.

Bullets left to right: LBT 310 175 .75, NOE 310 165 (30xcb), NOE 311 174 (Frank)

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OU812 posted this 2 weeks ago

The heavy Eagan design 200 grain plus bullets shoot very good also, but recoil is stout in the Remington Varmint Synthetic rifle. The lighter weight bullets above are less punishing and just as accurate @100 yards. Will do a test between all three bullets and post results. 20 grains of IMR 4759 will be used...and maybe Reloader 7. Alloy is 10 lbs linotype and 2 lbs pure lead. Bullet are seated long and pushed back into case when chambered (as pictured).

I want to say thanks to Ken C. for explaining what taper bumping is.

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OU812 posted this 5 days ago

Just a quick test without any load development. Used 19 grs of 4759 and 25 grs of Reloader 7. Impact on target says R7 was  creating more velocity. The LBT bullet shoots a little better.

Wet followed with dry patch was pushed down bore between each bullet tested. Barrel is very easy to clean and no hard fouling felt thru cleaning rod. 

Test was @100 yards, but 200 yards would be a better test.

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OU812 posted this 5 days ago

I worked 7 strait days of 12 hour nightshift before doing this test. Had only 2 hours of sleep before going to range. I really dislike  my job depressed

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frnkeore posted this 4 days ago

Excellent test, I'm looking forward to the completion of it.

It looks like the forward part of the nose is not, as cast on the Frank bullet.

What primers are you using with the 4759? I have the best results, using Rem 2 1/2 and F150's, with that powder.

Frank

 

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OU812 posted this 4 days ago

Frank,

The bullet deformation was caused by the extraction punch (strait 30 degree included taper) that I originally cut for the flat meplat Accurate bullets. I switched to your smaller diameter as cast 309-169-FN bullet for this test. It extracts from the taper bump die a little easier causing less deformation. Bumped bullets are extracted from die by hitting top of punch with plastic dead blow hammer.

I used Remington 9 1/2 primers, Lapua brass neck sized with Lee collet die.

The three bullets in picture (fat 314299, 309-169-FN, LBT) have been bumped. Notice no deformation of nose.

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OU812 posted this 4 days ago

I purchased the short chambered Shilen 1/10 twist chrome moly  barrel from Brownells. Chamber Head space was just .002 shorter than SAMMI specs after bolting on so I just left it alone (Remington 700 receiver was not blueprinted). Throated barrel by hand afterwards using the PTG .310 .75 degree per side reamer and snug slip fit  pilot bushing.

The blank 30 caliber PTG Die was cut using same taper reamer then shortened. Made the extraction stem from 6061 aluminum.

Bipod and Leupold 35 power scope helped lots.

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