new rifle with Undersized bore.

[OldIron86]

First post on THR, sorry if this is similar to any other post. I bought a new Henry Big Boy steel .357 magnum about a year ago. I've hunted and practiced with it quite a bit since then, and have decided to reload for it. So I slugged the barrel, lands measured .3553 and grooves measured .3533. I'm not a master of the craft, but that is 9mm diameter? should I load .355 bullets or stick with .357?

 

[Texas10mm]

The first thing I would question is your measuring ability.

Did you use calipers or a micrometer? Have you verified that the measuring device is accurate?

 

[rfwobbly]

Welcome Aboard !

Although the thoughts expressed above may sound harsh, it's a very valid point. Slugging a barrel is not easy and the tools required are expensive. So, I'd say the same thing, but go at it another way....

You say you've been shooting this rifle for a year. What is the diameter of the factory bullets that haven't given you any trouble during that time ? I'd say they are 0.357 to 0.358". And if those didn't give you any problems, then you should order the exact same diameter bullets for reloading.

I'd also suggest that you check out the jacketed and plated offerings from our friends at Rocky Mountain Reloading. Their 38/357 sized bullet offerings are extensive and nicely priced, all with FREE shipping.
https://www.rmrbullets.com/

Hope this helps.

 

[edwardware]

Since you'll be trying bullets, and working up loads, start with the obvious revolver-centric bullets.

As @Texas10mm and @rfwobbly said, I question your measurements. I have done some metrology work down to 0.0001", and I would not claim that level of precision outside of a lab setting, despite owning the tools to do so. A systemic error of 0.001 is easy to make, especially on a soft, round workpiece.

And if you're measurements are spot on +/-0.00005, I still suggest starting with a good olde fashion 158gr HiTek'd LSWC and a starting load of 2400 or similar. It's been working for a very long time.

 

[Jim Watson]

.3553 - .3533 = .0020"
Grooves only .0010" deep? I doubt it.

 

[Bfh_auto]

Welcome.
If your measurements are correct, this is why there are starting loads. A tight bore will give higher velocity and pressure with less powder. Accuracy shouldn't suffer from slightly over sized bullets.
Being a little over zealous with your measuring equipment can cause your reading to be on the small side. It's easy to crush soft lead.

 

[Walkalong]

Buy .357 jacketed or .358 lead and be happy.

Welcome to THR

 

[OldIron86]

Very good points. I may have not slugged the barrel properly. I used an aluminum rod and a .36 RB to slug. I work at Winchester now, maybe I'll chat up the guys in ballistics.

 

[OldIron86]

Thanks for the replies guys, I've got plenty of 125 grain sjhp and 158 jsp from my grandfathers reloading stock. I've got H110 and Titegroup to work with.

 

[Slamfire]

The first thing I would question is your measuring ability.

Did you use calipers or a micrometer? Have you verified that the measuring device is accurate?

Good point. Unless you have a gage block set, which I doubt



then you have no idea whether your measuring device has kept its calibration or not. I will guarantee that Henry has a calibration lab on site, and a calibration guy whose job it is to verify that all inspection and measuring devices are within calibration and traceable to a National Standard.

My gauge block set has the calibration check sheet with the temperature recorded as gauges expand in the heat.

 

[Blue68f100]

One thing that has not been mentioned is on odd number of lands/groves it requires the use of "V Anvils" micrometers in order to make proper contact. With flat anvils you will have a high/low condition due to the land/grooves.

 

[fxvr5]

First, your groove diameter measurement is within SAAMI specs for a 357 Magnum barrel. SAAMI lists the groove diameter as 0.355", but their bore diameter is 0.346". Tolerances are + 0.004", so a groove diameter up to 0.359" is still within spec.

I've yet to see published data of oversize bullets in handguns producing a clear increase in pressure. There is some old stuff that Speer once published indicating that oversize bullets did not produce much of a change in pressure.

You can try 9mm bullets if you like. Some of them can be very accurate in a 357 Magnum barrel.

 

[Texas10mm]

One thing that has not been mentioned is on odd number of lands/groves it requires the use of "V Anvils" micrometers in order to make proper contact. With flat anvils you will have a high/low condition due to the land/grooves.

Or you can wrap a piece of printer paper around the bullet and then subtract the thickness of the paper X2.

 

[jeeptim]

Welcome to the High Road!!
Don't get discouraged ...
My buddy just bought a Henry 45/70 lever and he's having trouble with a tight bore.
I would measure up some factory and do your best to match it up.
Best of luck