Today I finally did a pound cast to measure the freebore diameter of both my Remington 700 rifles chambered in 308 Winchester. First I filled two fired cases with mixed epoxy (Pacer brand finishing resin mixed 50/50 in Dixie cup) then hand seated a pure lead bullet in each case. Waited about 4 hours for epoxy to cure then chambered bullets. I use a 1/4” steel rod with tape wrapped around it as a guide and to pretect rifling and a rubber mallet to pound bullet to fit chamber. The Remington 700 Varmimt Sythetic chamber free bore measured .3115 The new Shillen barrel with minimum SAMMI chamber free bore measured .3101 Now I can size bullets to fit more accurately. What diameters do you guys recommend? I hear .0001 -.0005 under is best. Gas checks are a real nuisance, can a non gas checked bullet shoot just as accurately as a gas checked bullet. 
308 Chamber Pound Cast
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- Last Post 05 September 2014
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The Remington 700 VS with its larger .3115 NATO chamber will shoot most all bullets pretty good if they are sized .3113 and really loves the Harris design Lee 160 bullet with taper nose section. The tighter Shillen barreled gun really likes good fitting bore ride bullets, the RCBS 165 sil and Lyman 314299 sized .3095. I size bore ride section using a Redding .301 and .302 neck sizer die bushing resting on top of Lubramatic .358 size die installed. I turned down matching nose punches outer diameter from .303 to .300 so I can flip bullet over and press bullet back thru neck bushing after sizing nose. I size bullet bands and seat gas check dry so that gas check gets better grip, then I hand dip bullets in Alox thinned with mineral spirits and set bullets on wax paper (on their bases) to dry overnight. This lube method seems to work pretty good without having to clean too often. Is there a better lube.....SPG? 
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Veral Smith/LBT sells slugs to do a similar slug development, called a Rifle Throat Slug. Treatment of the empty case is different but the end result is probably the same as you've developed. If your muzzle velocities are on the high side then SPG might not be the best lube. SPG works good in BPCR loads but isn't universally applicable.
Tom
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Veral recommends using lead to fill case, but the epoxy is much easier for me (already have the epoxy). Just fill fired case with epoxy then push in PURE lead bullet until bullet is seated strait. You will see the thin epoxy being squeezed out when seating bullet by hand. wipe off excess epoxy with solvent soaked paper towel (mineral spirits or acetone).
Do any of you guys prefer shooting plain base rifle bullets? Are they just as accurate under 1900 fps if using linotype alloy?
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There is a LOT to the relationship between alloy hardness, bullet fit (to the chamber) and velocity. Want to see some good accuracy performance results with plain base bullets? Look into the CBA bench rest match results either on the CBA website or in the Fouling Shot, where shooters are using plain base bullets in the Plain Base Bullet rifle category and look at the alloy and velocity of their loads. Most are below 1400 fps and when the wind is kind they shoot great! Also look at the CBA National Records for Plin Base Rifles. And....the BPCR shooters where plain base is required by the rules, shoot great out to 500-meters and further (iron sights).
So yes, plain base can do just fine but I can't say for sure about a bolt action with plain base.
Have fun!
Tom
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Non gas checked bullets shoot just as accurately as gas checked bullets when the alloy is matched to the load ballistic pressure correctly. Gas checks are designed to extend the pressure range of an alloy farther.
To learn to select an alloy for plain based bullets based on the ballistic pressure of your load, study chapters 8, 9 and 10 of Modern Reloading Second Edition by Richard Lee. This will dummy proof the entire thing for life and answer all your questions with well researched fact that you can prove yourself confidently as I have and many others have. The system works completely and can be confidently used to end your alloy selection questions.
Source for book:
Other sources may be less expensive, so shop around too.
Gary
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tom, onondaga
I have that book and chart (page 107) says 22.0 bhn Linotype can handle max chamber pressure of around 28,000 psi. That equals to about 20 grs of my 4759 powder for a velocity of around 1900 fps. Slower burning powders will help even more. It also helps to use a lighter weight bullet if you want more velocity. Skipping the Gas Check sure would be nice. Now I have to decide what bullet to use. I may have the gas check shank enlarged on my RCBS 165 Sil bullet. This light weight bullet has a good bore ride diameter of .3015 cast with linotype. Thanks
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That will do it right for paper punching but Linotype gives cast bullets a poor reputation for hunting. Linotype doesn't expand on game at all and it shatters into fragments easily on impact with game also.
I use Lyman #2 for all my hunting bullets and I have another trick that extends the load pressure range . I use BPI Original filler with plain base bullets to pressures of about 35,000+ psi. the BPI forms a quasi gas check effectively. I use it in my .458 Win Mag and.500S&W rifle loads for Bear with plain base 340 and 350 gr bullets at 1700fps. Both Bear rifles do less than 1” at 50 yards.
There are plenty of plain base bullet design molds at Accurate Molds: http://www.accuratemolds.com/index.php
Gary
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Detox, all you need to use is Lyman #2. What is the twist on the Shilen? If it is the standard 1-10 then it is going to be a little harder to push it faster. Plain base you are looking at about 1500 fps for a max speed. Lino has nothing to do with it. It is erosion and flame cutting because of the PSI. That is why there are gas checks and jacketed bullets.
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Detox, all you need to use is Lyman #2. What is the twist on the Shilen? If it is the standard 1-10 then it is going to be a little harder to push it faster. Plain base you are looking at about 1500 fps for a max speed. Lino has nothing to do with it. It is erosion and flame cutting because of the PSI. That is why there are gas checks and jacketed bullets.
OK Tomme, I will take your advice. I also have a more desirable 1/12 twist barrel
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That will help with the 12 twist. I would skip the ALOX too. I would look into a good dip lube. I would also use a push through sizer as to not damage the base. That is critical on a flat base. Tom cuts very good molds. It will come out exactly like you want. Just make sure to let him know the exact alloy you plan to use.
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I have also used LBT Soft Blue Lube, it seems to have a higher melting point. Could not see accuracy difference between it and the Alox though. The Alox was just too simple to pass up and try. I need to test more.
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Here is a link to the commercial tumble lube from White Label Lube, Delux 45:45:10, I use it exclusively for every bullet, every caliber, every velocity I shoot and am very impressed:
At $15.00 a quart it is not even expensive either. I believe the only people that are unhappy with it are the people that use it incorrectly and invent their own methods. Used correctly it dries in 5 minutes, nearly clear and is tack free. It is a MAJOR improvement over Lee Liquid Alox.
Lubed correctly with 45:45:10, I know how to use this stuff correctly and get good bench rest accuracy results if you have any questions:
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You asked about bullet diameter, I custom hone Lee push through bullet sizing dies from the Lee Lube and Size Kits so my bullets are equal in diameter to chamber throat diameter for each individual rifle. I test bullet sizing and hone work with the bullets I actually use in the alloy I actually use until I get the right size equal to throat diameter with an un-lubed bullet.
Your chamber throat pound casting is interesting. I do simple chamber casting with an inexpensive chamber casting alloy, at $14.99 it is a reusable lifetime supply and there are good instructions right on the product page:
Gary
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Your White Label lube sounds interesting.
I have used the cerrosafe alloy from Brownells and diameter changes too much for me to get super accurate measurement. The pure lead pound cast holds its shape instantly and forever...with no voids.
Be sure to put a light coating of oil on bullet before doing a pound chamber cast for easier extraction.
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Yes the white label 45:45:10 is lower viscosity, but either can and should be thinned at any time the viscosity gets thicker than Hershey syrup. thin with mineral spirits, it is harmless to either product.
Gary
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Here is a better picture to show you the freebore length. The Factory Remington has a much longer 308 NATO length, about double the length of minimum SAMMI chamber length of .090 308 NATO left..............308 minimum SAMMI right. Notice the Remington barrel on left has more narrow .040 wide rifling lands. The Shillen's rifling lands measures .060 wide. The chamber cast really helps you understand why some cast bullet designs will work better than others. I can easily see why the larger Remington throat likes the LEE 160gr bullet with its .312 wide base and tapered nose.
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