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Throat Reaming Guide

PracticalTactical

I have always been uncomfortable with the accuracy of throating reamers, so I came up with this system to ensure proper alignment in two places for the throating reamer.

The conical bushing indexes off the bolt nose clearance hole.

Hand reaming a throat is generally frowned upon, but with this system, you can ream the throat by hand with confidence.

Just thought I'd throw the idea out into the wild if you see any use for it.

Here's a few pics.
 

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Has anyone ordered a specific sized custom Uni-Throater lately and if so what was the lead time or how long did it take to get it?

I'd like to order a couple but I don't want to mess with PTG if they can't ship in a known reasonable time frame. Reasonable would be what the others like JGS or Manson have for lead times right now.
 
JGS/Manson likely have them on the shelf. I'd post a wanted in the forums for the ones you want if you want the PTG kit... That's how I got the ones I wanted... Seems a lot of people buy them and use them once and that's it.
 
Just an idea... but you could use a length of (maybe copper) tube and slide it over a Manson or JGS throating reamer to control your depth. Just cut the tube to suit your free bore length.

Or just make a lock ring with a set screw hole. Crappy example but, something like this.

I think they are called drill bit depth stops.

s-l1600.jpg
 
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Here's how I use Manson's throaters. First make an extension, 3/8" steel rod with a set screw. Might have to grind a flat on the reamer for this. Then I use a Sinclair neck turner case holder as the holder on the extension. This will probably drive you nuts. I use a drill chuck in the tailstock as my reamer holder and pusher. Tighten the chuck then just crack it open enough to allow the reamer to spin. Hopefully I have a dummy round. Easy into to it until the reamer just starts to cut. Stop and take a headspace measurement using the dummy round as a gage. Do the math then when the reamer starts to cut again feed in to that number. Just so I don't make the phone ring if the dummy round is close to mag length I'll stop a little short.
If the barrel is on the action I have a rod guide with a 3/8" reamed hole. 3/8" T-handle extension with a stop that goes through that. Rod guide stops on the barrel then set the stop with calipers. If you're in a good mood you can use a stripped bolt with a dummy round and work your way through the numbers to get the length right.
 
DaveTooley said:
Here's how I use Manson's throaters. First make an extension, 3/8" steel rod with a set screw. Might have to grind a flat on the reamer for this. Then I use a Sinclair neck turner case holder as the holder on the extension. This will probably drive you nuts. I use a drill chuck in the tailstock as my reamer holder and pusher. Tighten the chuck then just crack it open enough to allow the reamer to spin. Hopefully I have a dummy round. Easy into to it until the reamer just starts to cut. Stop and take a headspace measurement using the dummy round as a gage. Do the math then when the reamer starts to cut again feed in to that number. Just so I don't make the phone ring if the dummy round is close to mag length I'll stop a little short.
If the barrel is on the action I have a rod guide with a 3/8" reamed hole. 3/8" T-handle extension with a stop that goes through that. Rod guide stops on the barrel then set the stop with calipers. If you're in a good mood you can use a stripped bolt with a dummy round and work your way through the numbers to get the length right.
Click to expand...
Have you ever made a concerted effort to compare the free bore diameter on the barrel to the diameter on your throating reamer after doing this?

You are describing almost exactly what I used to do, until I realized my free bore diameters were both over sized and trumpet mouthed. That got me into evaluating the alignment errors between the quill and the spindle and how it changed as the quill was extended and retracted. Or the repeatability when the tail stock is moved back and forth.

Reamer manufacturers always make the reamers over size so you don't get an overly tight throat that essentially becomes a seating die when you chamber a round. Then to that clearance, you add a little alignment error on your engine lathe, plus a little side pressure so you cut heavy on one flute. What you end up with is a sloppy free bore diameter that is useless to ensure bullet alignment to the rifling.

Sure the front of the bullet is aligned by the taper in the throat, but the back of the bullet can be just about anywhere. No surprise when the bullet flies wonky and velocity spreads are not as low as expected. Fast rounds enter the rifling along the center line and slow rounds hit the rifling on a slight angle. That angular difference affects the engraving force levels and affects your velocity spreads before the bullet can move a tenth of an inch down the barrel.

Few hunters would respect the difference but long throat VLD F Class shooters will certainly notice the performance difference.
 
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A couple of things

"Reamer manufacturers always make the reamers over size so you don't get an overly tight throat that essentially becomes a seating die when you chamber a round."

They make them to a spec. Usually -.0000 + a few tenths. Everything has to have manufacturing tolerances.

"What you end up with is a sloppy free bore diameter that is useless to ensure bullet alignment to the rifling."

I'm not sure useless is the right word. I have proven to myself that concentricty vs diameter is paramount to accuracy. Tight FB's can induce many small complications that can be difficult to identify. Even harder to manage. I despise tight FB's. I get asked by many of my OEM customers I do accuracy barrels for what 308 Win reamer I use. The reason they ask is they can't duplicate the performance of my barrels. My answer is SAAMI spec reamer. A .310" FB. Unless you spec out the FB diameter most throating reamers are larger than many finish reamers.
Is using a throating reamer the best way? No, a finish reamer with a proper throat is always the best way. I would only use a throating reamer on a match rifle as a last resort. I'm not a fan of long long FB's. Just never worked for me. I'm not concerned about the alignment of my tailstock in this application. It never moves more than 1/2 inch and the reamer floats and the cutting forces center the reamer.
All these things we know or think we know. Can we shoot the difference?
 
DaveTooley said:
A couple of things

"Reamer manufacturers always make the reamers over size so you don't get an overly tight throat that essentially becomes a seating die when you chamber a round."

They make them to a spec. Usually -.0000 + a few tenths. Everything has to have manufacturing tolerances.

"What you end up with is a sloppy free bore diameter that is useless to ensure bullet alignment to the rifling."

I'm not sure useless is the right word. I have proven to myself that concentricty vs diameter is paramount to accuracy. Tight FB's can induce many small complications that can be difficult to identify. Even harder to manage. I despise tight FB's. I get asked by many of my OEM customers I do accuracy barrels for what 308 Win reamer I use. The reason they ask is they can't duplicate the performance of my barrels. My answer is SAAMI spec reamer. A .310" FB. Unless you spec out the FB diameter most throating reamers are larger than many finish reamers.
Is using a throating reamer the best way? No, a finish reamer with a proper throat is always the best way. I would only use a throating reamer on a match rifle as a last resort. I'm not a fan of long long FB's. Just never worked for me. I'm not concerned about the alignment of my tailstock in this application. It never moves more than 1/2 inch and the reamer floats and the cutting forces center the reamer.
All these things we know or think we know. Can we shoot the difference?
Click to expand...
For every expert there is an equal and opposite expert apparently.

We are on totally opposite sides of your point. Keep in mind that my focus is exclusively accuracy for long heavy VLD bullets. Short free bores are death for heavy VLDs as far as I'm concerned. It forces the bullet too deep into the case, that robs powder capacity and prohibits the free bore from guiding the bearing surface straight into the rifling.

Then what, neck turn brass to help provide the missing alignment... That's certainly an option, but not required if the free bore is tight. Even with a tight free bore there may be a benefit extracted by neck turning at the very least to stabilize neck tension.

As for concentricity problems, certainly the easy way to maintain that is by throating with your body reamer, but while you are pecking away trying to set your headspace you are free wheeling the free bore diameter larger and larger the more time it dwells there. Good on you if that's what you want, but hell if I want it.

I have had too many expensive barrels not shoot well over the years and I'm tired of barrel fitters injecting their opinions and delivering results that are less than I expect. Then the poor barrel maker conveniently gets the blame.

The last two barrels I traditionally chambered for 223 shot between 3/8 and 1/2" at 100 yards with 88 grain ELDMs. I like 0.200 free bore for 223. Using the bushing system to throat the rifle on my first barrel out of the first 20 shots, it shot three consecutive groups under 0.150" at 100 yards using 88 grain ELDMs. Further testing to be done, but the improvement is obvious.
 
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Theres a current 1kyd IBS group agg record on the books, that barrel was throated multiple times through the year by hand by its owner. As in, the smallest 10 targets ever shot. In fact theres LOTS of records with those sloppy freebore diameters I use. Most guys would be surprised how big my freebore diameters are specd. Dave is correct.
 
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You are all entitled to your opinions.

I have my own and will continue to test using the tightest safe freebore diameters I can get away will and prove the point to myself.

Sometimes people do well despite the weaknesses they have and not because of them.

Jack Nicklaus was once a superstar but he could not have been competitive against a swing like Tiger Woods.
 
PracticalTactical said:
Using the bushing system to throat the rifle on my first barrel out of the first 20 shots, it shot three consecutive groups under 0.150" at 100 yards using 88 grain ELDMs. Further testing to be done, but the improvement is obvious.
Click to expand...
Good stuff. But, still anecdotal at the end of the day since the barrel itself is, and will always be, a variable as no two are precisely the same.
I like the concept. I use a adapter bushing to be able to use throaters with a micrometer stop, but this method relies on a snug bushing to maintain alignment. I'm going to look into adapting the micrometer stop to maintain perpendicularity beyond relying solely on the bushing.
 
tobnpr said:
Good stuff. But, still anecdotal at the end of the day since the barrel itself is, and will always be, a variable as no two are precisely the same.
I like the concept. I use a adapter bushing to be able to use throaters with a micrometer stop, but this method relies on a snug bushing to maintain alignment. I'm going to look into adapting the micrometer stop to maintain perpendicularity beyond relying solely on the bushing.
Click to expand...

What are the possibilities that could be true?

A) I got lucky and this barrel is better than any other I got over the last 10 years and the tight throat chamber makes no difference.
B) The barrel is about the same as other barrels I got over the last 10 years and the tight throat chamber is the reason it shoots better than others.
C) The barrel is better than most and the tight throat chamber makes the most of it.

Again, my interest is in the context of long heavy VLD bullets, and in my case using 223 or 308 for F Class FTR. Meaning I have limited case capacity that requires a long throat to get performance with heavy projectiles.

Time will tell. Light winds expected on Saturday, 30 rounds on the bench ready for testing.
 
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