The Rochefort/Manning
.45-70 Chamber-Throating Reamer
or
Another one of our series in the myriad ways you too can become proficient in
Home Gunsmithing
by Miles
Well, just when you thought we're just posting Mike's articles, I've come up with something for the enterprising home gunsmithee. A year or so ago fellow Sixgunner Alan Rochefort posted that he had designed a widget to ream the throat on tight .45-70 lever-action rifles without the need to remove the barrel!
I had bought a Browning '86 the year before and was loading Hornady's 350gr. round nose bullet. This necessitated the filing of the nose flat as I didn't want to have a chain fire in the magazine.
About six months later, Hornady introduced their 350gr Flat Point! I thought that my prayers had been answered and ordered several boxes. A problem developed, however, when I tried to shoot them. When the bullets were seated and crimped in the cannelure, the cartridges would not fully chamber!
If you look closely at the
picture of the two different bullets, 
you'll notice that the flat-point has a slightly "fatter" ogive.
This kept the bolt out of battery about .050 inch. I later heard that the
bullet was designed specifically for the new .450 marlin and that those rifles,
and late production Marlins do not have this chambering problem. I do know
of one early M95 Marlin that has the same problem that my Browning had.
At the time, I had really only one alternative
seat the bullet deeper in the case, past the cannelure, and put a strong crimp
to keep the bullet from being pushed deeper into the case.
When I read the post from Alan about the reamer, I had E-mail on the way as fast as I could type. When the shipping tube arrived, Dad & I hot-footed it down to the shop to see what we had. Alan and I had talked over the phone for quite a while as he explained the design and use of the reamer and I was sure we could get the job done quickly. I actually doubled the time it took due to the need to photograph the process. REALLY, IT'S THAT FAST!
The set has two rods of different lengths for different barrels, a combination wrench and the reamer.
Secure the receiver in a padded bench vise
Slide the rod down the barrel.
Screw in the reamer and using the combination wrench
tighten it down with a padded set of Vise-Grips. Pull the reamer into the chamber until it stops on the rifling leade. Mark the rod with a "sharpie" pen at the end of the muzzle so you can tell how far you've reamed.
Lubricate the reamer with a high quality machine cutting oil. Then, pull it very slowly (it doesn't take much pressure to cut the new leade) and turn the rod counterclockwise (as you're looking at it from the muzzle towards the receiver) at the same time until you've lengthened the throat the desired amount.
The cartridge that wouldn't fully chamber, now DOES.
Some people might be concerned that this could possibly have a deleterious effect on accuracy. I submit the following targets for you.
"Before Target" with the RN bullets
"After target" The lowest shot was my first with a new load and the FP bullets. I raised the rear sight one notch, then fired three for a group. The weather conditions were: Temp in the low 70s with VERY high and gusty winds.
Both groups were fired at the JbarT Ranch range at 75 yards, off the Kelly-Taffin machine rest.
Alan is done with it, and passed it on to me. Now, I'm done with it and will pass it on to whichever Sixgunner is interested. The proviso is: Neither I nor Alan will be held responsible if you goof and ruin your barrel. His shoots fine. Mine shoots fine. Yours should too.
Thank you for your kind attention, we now return you to our regular programming.
03-09-03