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Forcing cone HELP

This is a discussion on Forcing cone HELP within the Gunsmithing forums, part of the Firearm Forum category; Cut 11 degree forcing cone in my GP100/.357, was paying attention to depth to remove factory machining grooves and not the outside diameter. According to ...


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Old March 11th, 2017, 07:43 AM   #1
 
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Forcing cone HELP

Cut 11 degree forcing cone in my GP100/.357, was paying attention to depth to remove factory machining grooves and not the outside diameter.

According to Brownells instruction the OD of cone should be no larger than .020 of bullet diameter (which is .358) for an OD of .378.

The OD at barrel face is now .040 (or .032 over bullet). Is this safe to shoot or is new barrel in order??

Pics of before and after attached.
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Old March 11th, 2017, 08:06 AM   #2
 
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I think you went a little overboard with the cutter but it's done now. As for safety, I don't think it will be unsafe but you'll probably see a slight decrease in velocity. It may work fine with lead bullets, time will tell.

If you have a good gunsmith nearby you could probably get him to set that barrel back a thread or two and gain enough barrel to re-face the breach and be in good shape.

OR, if you don't mind being chastised by Ruger & paying for a new barrel, you could send it back to the factory.
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Old March 12th, 2017, 06:21 AM   #3
 
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Thanks for the reply P&P.

Only shoot lead, coated 158 gr SWC which leaded forcing cone consistently but only a small patch at 7 o'clock position which is why I decided to recut cone to 11 degrees, hoping to decrease leading and improve accuracy.

Went to range yesterday and definitely lost velocity with new cut as groups were all 4" low at 25 yards. Leading is much worse and around entire circumference of cone. No lead spitting and no lead on cylinder face or frame.
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Old March 12th, 2017, 06:40 AM   #4
 
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Quote:
Originally Posted by max38 View Post
Thanks for the reply P&P.

Only shoot lead, coated 158 gr SWC which leaded forcing cone consistently but only a small patch at 7 o'clock position which is why I decided to recut cone to 11 degrees, hoping to decrease leading and improve accuracy.

Went to range yesterday and definitely lost velocity with new cut as groups were all 4" low at 25 yards. Leading is much worse and around entire circumference of cone. No lead spitting and no lead on cylinder face or frame.
If you're getting leading around the entire circumference of the cone you probably have two things going on:
The bullet is too small (tight throats on the cylinder?)
and
That big funnel of a forcing cone is allowing a lot of gas past the bullet before it makes it to the rifling. That gas cutting of the bullet is the source of that leading.

You could check the throats and ream them if they are smaller than the groove diameter of your barrel. That may fix your leading if you're lucky.
If not, I'd consider getting that barrel set back a thread and re-cutting the breach face of the barrel (a flat 90 degree cut) to re-establish the correct barrel to cylinder gap. That may buy you enough distance to remediate that over cut cone.
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Old March 22nd, 2017, 11:57 PM   #5
 
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Forcing cone HELP

But if he is going to reach the lands and grooves, and avoid a compound angle, I do not think he can cut less.
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Old March 23rd, 2017, 03:02 AM   #6
 
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But if he is going to reach the lands and grooves, and avoid a compound angle, I do not think he can cut less.
Exactly!!

Revolver is now in the good hands of Ruger for barrel replacement.
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Old March 23rd, 2017, 04:18 AM   #7
 
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Ruger will take care of it but the solution is either going to be setting the barrel back or replacing the barrel. Because they have a large supply of barrels on hand, it would probably be less expensive (in terms of time) for Ruger to simply replace the barrel.
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Old March 23rd, 2017, 07:23 AM   #8
 
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Originally Posted by Petrol and Powder View Post
You could check the throats and ream them if they are smaller than the groove diameter of your barrel. That may fix your leading if you're lucky.
If I remember correctly getting the cylinder throats opened to .3585 stopped the forcing cone leading on my GP100.
I also had the forcing cone cut to 11 degrees just like yours. It still shoots good.

Maybe you could have a Match Champion barrel installed? Wonder how much more that would cost?
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Old March 23rd, 2017, 06:36 PM   #9
 
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Exactly!!

.

Unless you are shooting very short bullets I think it would have been fine. Adjust the bullet, powder, or charge. I reamed my forcing cone to the lands. The cut was short but a little wide. But the .45 lead bullet seals before it fully leaves the chamber. I also added a Belt Mtn base pin which took some slack out of the cylinder fit.

Let us know what Ruger does. Please.



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