Bullet base

[RMulhern]

Is there anyone here that thinks that the base thickness or "lack of sufficient thickness" plays a part in being conducive to "blowby"? With the larger diameter cases...there are those that think this is/can be a problem and some shooters I know have changed their mould designs to pour thicker bases! One claims that it solved accuracy problems for several guys within his group.

Your thoughts?

[kevin harris]

Sharpsman,

In my humble opinion(and I'm open for correction), the base thickness of the bullet plays a significant roll with blow-by however I think a more major part is played with the wad material used eg. thickness, makeup(polly, veg-fiber, gaskett material from auto parts store, etc.).

More thoughts are welcome

[Lead Pot]

Sharpsman.
I have a PJ mould in .40 caliber that has a .115 thick base,and had a little leading problem with that bullet with 30-1 alloy,and a .30 veg-fiber wad.I had to change to a .60 and added another .20 card.That solved the problem.

With my SB mould it has .155 base,and I dont have a problem with that one with a .60 wad.

I'm using a 20-1 alloy now in the .40 caliber and getting allong fine with that.I think with the 16 twist in the .40 caliber needs a little harder alloy.
Some day I will get enough currage up and fire a few rounds into my enlaws swimming pool to recover a good bullet to see just how much blowby those thin soft based bullets have.

Kurt

[Trigger Dr]

I am a Hunter and have not shot for target accuracy other than sighting in for hunting ranges. I cannot speak for the difference the base thickness would have on accuracy. However, that being said, I have a 4 cavity Lyman 457406 mould that I have used for 30+ years. It is a gas check bullet weighing 482 gr when cast with the Lyman #2 alloy. I had Ron Heilman recut the 2 center cavities to remove the gas check area and increase the base driving band from .085 to .225. As far as hunting accuracy, my groups have tightened a bit. Is this from the additional area on the base band, or the fact that I got new glasses? As far as leading, what little leading that was there with other loads, I now have NO Leading that I can detect when shooting the 457406 Modified. This bullet in 30 : 1 alloy casts 513 gr. I have not been able to find this mould for several years in any catalog, ad presume that it it no longer in production. This mould was advertised as being capable of casting bullets that could be shot with or without the gas check in place. I have shot them both ways and could see little if any difference in hunting accuracy, but there was a trace of leading the first few inches past the chamber.

Trigger Dr

[kevin harris]

Trigger Dr.


I have not shot bp as long as you via hunting or targets, but in my humble opinion since you increased the base thickness you increased the resistance to gas cutting on on the bullet. Therefore less leading and greater accuracy. Right now I have 48rounds of lazercast 405gr. bullets loaded with an .030 card wad to help protect the base of the bullet, however those bullets have a beveled base and gascut terrible bad. I melted the hard lube off and re-lubed with bp lube to help with powder fouling so I am eger to find out what is going to happen. The reaon for this agony is that even with the hard lube and 5 rounds at 200 yds. I shot a two inch group with black powder.

[Trigger Dr]

Kevin Harris,
I did some testing for Keith at Lazer cast when he was just starting to make the .458 bullets. I told him at the time that they were too hard, and that penetration was excessive, with fragmentation with the slightest touch on bone, woor or even gristle. No change was made as he is casting for a much larger market than BPCR.
Trigger Dr

[JAGG]

Before you start cutting the bases of your bullet moulds thicker , check you alloys as to whether they will expand into your rifling first ! If you have a hard alloy and a slightly under size bullet that won't expand into the grooves then , you will get leading and blowby . You have to just change your alloys to conform to the pressures of the load ! With an over sized barrel groove and an under size lead /tin alloy only bullet , you can still get excellent accuracy , and thats is how many of the old rifles were made years ago to use the powder pressure of BP to bump up the bullet to match the barrel grooves and be a form fit . JAGG

[RMulhern]

Thanks guys! I figure we can all....still learn from each other!

[kevin harris]

And thats what its all about; shooters helping shooters and making friends along the way