Cast boolits in micro groove barrels

Ok, I know this topic has come up before but I can't find any threads on it.

I am trying to come up with a good load for my brother's Marlin Guide Gun in 45-70. I have loaded some 405 grain flat point lead boolits (actually weigh 415 gr. out of a Lee mold) and it shoots well. The allow is wheel weight PB dropped in water. Do I need to be concerned about leading in this barrel or not? Am I going to need to change to gas checked boolits? Just looking for insight from other Marlin owners. Thanks and sorry if this has been answered elsewhere. Will

I have not tried it yet, but the powder coat guys claim to get excellent results in micro groove barrels.

Greetings
Have a couple Micro-groovers. The key to me is load a fat boolit. If my 45-70 will chamber a .462 I would load it. My .357 chambers .360+ so that's what I feed it. No leading problems.
Plus I do not start with the hardest mix possible. In rifles I find 50/50 works real good unless I am looking to load near max base pressures.
The starting point is get a throat measurement. If the throat is .460 I would want at least a .461 boolit IF it will chamber. This is my proceedure for any type rifling especially plain base.
Generally a boolit diameter +.002 over bore will get all the grip you need.. but again the throat area comes first. My old 45-60 has a .464+ throat and a .460 groove. Those boolits really get a squeeze getting into the barrel but it sure shoots good without any leading.
Get a good tight grip in a barrel and it will fly fine.
Mike in ILL.

I shoot nothing but plain based cast bullets in my micro grooved marlin 45-70 these days. As mentioned the trick is to use the right size (big enough), my barrel slugged out to .459 and I get the best results and a clean barrel with .461 cast

My experience exactly

Plus.

Water dropping is not gaining you anything. On the other hand it is not hurting anything.
I personally would not do it.

.

Big/clean sharp base wins the day!
1Shirt!

You said it shoots well. What more info do you need?
Size them large enough and all will be fine. I have gone as fast as 1700 with a plain base in my Marlin.

My marlin is a 30-30, but the same rules apply. I'm sizing just under 0.002" over, straight wheel weight, air cooled. In my case I'm using a gas checked boolit, but as you will see, a large group of shooter marlin shooters are enjoying success with plain based as well.
In short, if the rifle is shooting well with the arraignment you have now, with no leading, then there is no problem to repair.

My own micro groove 1895 does just fine with commercial .458 plain base slugs. When I start casting for it I'll probably go with .459. My .30-30's do great with .310.

Thanks to all for the replies and advise. I will try to slug the barrel before going any further.

My Marlin .30-30 slugs right at .308 and I run them through a .311 sizer just to seat the GC. It doesn't size the boolit and they shoot just fine with a 50/50 WW Pb mix. If I cast to hard they will lead just a little if pushed so I think I need a bigger diameter mold.

Quote:

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Originally Posted by webradbury

Do I need to be concerned about leading in this barrel or not? Am I going to need to change to gas checked boolits?

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Who knows? Predicting results is a set up for disappointment. I do know generally that MG bores shoot Jbullets really well via my own experiences. I know through my own experiences that some fairly soft plain base bullets shoot really well in MG bores with reasonably light loads. But, gas checks tend to solve many problems as pressures and velocities increase with increases in smokeless loads. You'll be the first to know during your testing of various combinations. The learning curve will sharpen through your own experience. Is leading dangerous?- nope. Is not using a gas check dangerous?- nope.

I have a 336W micro and it shoots cast very accurately both PB an GC sized .309"!

Are you sure your brothers rifle has a MicroGroove barrel. I believe all the Guide Guns have Ballard rifling, My early ported Guide Gun made in 1999 certainly does.
Doesn't make a whole lot of difference tho. Slug the bore, make a chamber cast & find a boolit that fits the rifle. Also use a good lube & adjust your alloy to the velocity/pressure & you shouldn't have leading issues unless there are problems with the barrel burrs, bulges etc.

Aje