Taper Bumping

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OU812 posted this 13 May 2018

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 .80, NOE 310 165 (30xcb), NOE 311 174 (Frank)

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OU812 posted this 13 May 2018

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 22 May 2018

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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frnkeore posted this 23 May 2018

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 23 May 2018

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 23 May 2018

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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OU812 posted this 02 June 2018

Today I tried several 3 shot groups with several different powders. Best group was 29 grains of Varget behind Franks bullet. Will go back and try to duplicate group. Firm and consistent hold on rifle is very hard for me to duplicate. No fouling shot fired before shooting best group of .25"

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OU812 posted this 03 June 2018

Bullets are first sized nose first .311 in the Lee die, then lubed in the RCBS Lube a matic using .311 die, then bumped in the .310 diameter bump die.

Somebody mentioned that more lube or lube grooves is easier on the throat (less throat erosion). Bullet shoots good with all lube grooves filled with LBT soft lube.

I am going to try the plain base version with filler (used Maxwell House).

Plain base version weighs 162.5, Gas check version weighs 165.0 with my alloy (5 lbs Lino, 1 lb lead)

 

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frnkeore posted this 03 June 2018

Excellent results, I'm impressed

 

Frank

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Maven posted this 03 June 2018

Ed, I purchased a taper-bump die for my .30-06 from Ed Wosika years ago.  It bumps undersized CB's to .310" (body) x .302" (nose) and leaves the GC perfectly flat.  It turned my undersized Lee C-309-180-R and Ly. #311291 into excellent shooters.  It also works very well for removing the GC shank and leaving a flat base when you want to try a plain base version of a given CB, albeit with greatly reduced loads.

I should add that there hasn't been a CB I tried, tapered & bumped as mentioned above, that has shot worse, i.e., less accurately, than its "unimproved" brethren, with or without GC's.

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OU812 posted this 03 June 2018

Actually I am squeezing down an oversize bullet to fit tapered throat and bore. Is swaging the correct term … not bumping? Gas check is not perfectly flat after swaging these bullets.

 

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John Alexander posted this 04 June 2018

Swaging is the correct term whether you are reducing the diameter or upsetting it to a larger diameter. Bumping might be called a slang term that cast bullet shooters invented when they started "fixing" undersize noses in lubrisizers by upsetting them to a larger diameter.

John

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dbarron posted this 04 June 2018

Dave Corbin defines "swaging" as increasing diameter and reduction as "drawing".  Maybe a useful distinction.  Whatever.

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OU812 posted this 15 June 2018

Found another powder that works pretty good … 28grs N135. I will go back and compare these four loads that shoot good (18.5grs 4759, 23grs R7, 29grs Varget, 28grs N135). 

I tried briefly using used dried coffee as filler with plain base bullets. Groups were very large so stopped test. May try again latter.

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OU812 posted this 20 June 2018

Groups start to open after 5 shots. I will experiment with lube and lube volume next (Franks bullet).

Left target: 1758fps,19grs 4759

Right target: 1905fps, 23grs R7

I also learned the rear shooting bag needs to be packed tight with sand.

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Geargnasher posted this 20 June 2018

Have you been using a bipod to shoot all those groups?

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OU812 posted this 20 June 2018

I always use a bipod for load development. Lots easier to carry to range than my heavy Hart front rest.

I wonder if strait White Lithium grease would work as lube? I could smear into grooves by hand.

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frnkeore posted this 20 June 2018

I use a lube for HV that is 30% lithium and the rest BW. At that ratio, it's still fairly soft. It can also be used in pan lubing and is the only way that I lube.

Initially, when you mix it, it takes a lot of stiring to get the lithium mixed but, it stays mixed after that.

What lube are you using?

Frank

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OU812 posted this 21 June 2018

I use LBT Soft. I will try filling less lube grooves or using different grooves...such as filling the two most forward bands.

I wonder if thin SPG black powder lube would work?

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Geargnasher posted this 21 June 2018

I always use a bipod for load development. Lots easier to carry to range than my heavy Hart front rest.

I wonder if strait White Lithium grease would work as lube? I could smear into grooves by hand.

 

No doubt easier to tote about, but you're a heck of a lot more accomplished with bipod technique than I am (and the large majority of shooters) if you can refine sub-moa loads while using one and make sense of the data.  I'd love to see how well you can do with your fine Hart rest.

I have used straight lithium and lithium complex grease in many forms, from NLGI #2 to 6 and off the scale, both commercial and compounded myself.  Universally, above about 12-1400 fps in .30-45 caliber,  I found accuracy to degrade and barrel deposits to form unless a minimum of 10% wax is present.  Similar is true of sodium grease and especially the non-soap thickeners such as bentone, fumed silica, and various forms of carbon (other than carbon which has been specially treated with soap).  The wax isn't your problem, it's probably too much of the lube you're using, and if anything, go to a lube which has NO soap in it, such as beeswax/vaseline, Darr's lube, or similar to eliminate soap residue as a problem rather than going the other direction......but......just because I came to these conclusions won't mean you and your rifle will, so try it!

A technique I employed during lube testing occasionally is to patch out after every shot, you may find as I did years ago that using too much LBT lube for your pressure and velocity window can leave heavy, stiff carbon residue in the bore which can be pushed out with a dry patch after every shot, and doing that while experimenting with putting different amounts of lube on the bullet will tell you something. 

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frnkeore posted this 21 June 2018

As for SPG, I haven't heard of it used in any loading, over 1500 fps. It's used a lot in BP loading but, in Schuetzen matches (1400 - 1600 fps), it's not used that often.

Regarding Darr Lube(50/50 Vas/paraffin), I used it for 10 years. It wonderful, under 1500 fps and under 85 deg (leads horribly at 100 deg). I had to keep my lubed bullets in a small ice chest at above 80. It does not work at >1900 fps, because it wasn't accurate.

I tried Vas/BW, also but at this late date, I don't remember why I didn't use it at 1900+ but, if it showed good results, I would have remembered.

The only lube (home brew types) that worked above 1900 fps was lith/BW. I first tried it 50/50 but, it was way to tin, for my liking so, I cut it to 30% and it worked well and produced good GC groups up to 2250 fps.

I think a good, all round lube is 50/50 BW/alox or the original NRA formula.It works to 2000 fps or more. I now use 25/75 BW/ alox and will increase the BW to 30% later, to stiffen it a little. I've shot extremely good groups and scores, with it but, I don't shoot at 2000 fps.

Frank

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Ken Campbell Iowa posted this 21 June 2018

i played with straight lithium .... filled grooves ..... and it shot well after the first shot .... but that first shot was a "" flier "" .... a big flyer .....  and if i waited 5 minutes, the first shot was again way out, the rest shot well  ... i gave up, never could explain that ...

.... but does hint that barrel conditioning might be a cause of mysterious mischief in our cast groups ...

***************

i might mention that i still play with moly lubes often ..   i " think " that they maintain static barrel condition forever .... but never quite as accurate as standard lubes .  maybe perfect for an afternoon of plinking ... but maybe not absolute best for a record target ....  but then i see jim scearcy uses some lyman moly .... that is more waxy than my softer homemade moly glop.  ( mine is andok c bearing grease and 20-40 % moly powder )

oh, with the moly it takes almost none at all, at least for my 1400 fps plinkers.  the more you use the worse it shoots.

ken, still waiting for those 3rd and 4th rules for cast accuracy ...

 

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Geargnasher posted this 21 June 2018

Felix Robbins' lube formula is so far the best accuracy lube for rifles I've ever used.  Maintains consistency for several thousand rounds with no cleaning or patching whatsoever...my mileage.  There must be some reason people aren't using it much in matches, but that doesn't mean it isn't good for some of us.  Below 2000 fps and below 90°F it's a good idea to add Vaseline to it at one rounded tablespoon per pound to help with lube jettison, otherwise you might see a lot of flyers and lube "boogers" splattered on your 100-yard targets.  

I still think the LBT soft is fine, just maybe only lube the rear two grooves and leave the rest empty.  Metal needs somewhere to displace as the bumped cone becomes a smaller cylinder, and if the front grooves are full of lube, more bullet distortion will take place.

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OU812 posted this 2 weeks ago

Here are groups shot using the taper bumped 30XCB bullet and Reloader 7. The diluted linotype shot better than water quenched WW in this test. Lots more to try and have more loaded for testing. All load combinations shoot better because of taper bumping

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OU812 posted this 2 weeks ago

Using two size versions of Frank,s bullet (.309, .311). I wanted to see if too much sizing makes a difference. Bullets were sized to .311 nose first in Lee sizer. Then lubed using Felix lube supplied by Gearnasher.

The .309 advertised bullet cast .3115 diameter with Linotype alloy

The .311 advertised bullet cast .313 diameter with Linotype alloy

Both bullets shot well, so I could not see difference. Felix lube works really well and no leading.

Still using bipod and rear sandbag. Retical was shakey (shooter error)

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frnkeore posted this 2 weeks ago

Thank you for the test. I'm glad to see that they are competitive with each other I designed the .309 bullet, specifically for match rifle chambers, with freebores of .3085 to .3082 and not the standard 308 Win freebore of .310.

The other criteria was for it to be lighter that what is being used, to reduce recoil and fatigue but, still have a high BC.

Al (NOE) added the larger bullet for the standard chamber. I think that you wrote that yours is a match chamber? If so, what is the freebore and leade angle?

Thank you, again,

Frank

 

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OU812 posted this 2 weeks ago

I purchased the Shilen short chambered barrel from Brownells . It has a standard loose 308 Winchester chamber(throat area in front of case mouth was uncut from factory) . All I did was adjust the head space with PTG recoil lug (.002 shorter than SAMMI). Then cut tapered throat by hand using PTG tapered reamer (.75 taper per side, .310 diameter). I cut just deep enough so that my seated LBT tapered bullet would fit 308 magazine well. Maybe .050 free bore.

BTW I cleaned barrel every 10 shots for test, but this lube allows more shots without cleaning. I filled bottom 3 lube grooves for test.

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Scearcy posted this 2 weeks ago

Great info. This is a very enjoyable thread.

Jim

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OU812 posted this 2 weeks ago

Thank You !

My alloy is Linotype (spacers only). Not as hard as real linotype. About 17-18 bhn.

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OU812 posted this 2 weeks ago

Today I cast 110 of Frank's bullets using my new RCBS pot. There were near zero defects or culls using the ladle. I separated bullets front and rear cavity.

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