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I been loading for a long time but haven’t run across this before. The rifle is a Ruger American Predator 6mm Creedmoor.

To determine bullet seating depth I do like a lot of folks, using a Stoney Point gauge, insert bullet in the modified case, slide into chamber, move bullet forward until it touches the lands and start adjusting COAL from there.

What I’ve run into is what I think is a tight throat. After inserting the modified case into the chamber and start to move the bullet forward, I feel substantial resistance after only a few thousandths then I can push it on in to a hard stop which is I assume to be the lands.

Is there anyway to determine if the throat is undersized?

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the throats are typically cut as a specific angle…

Check that your bullet is passing smoothly through your OAL cartridge, sometimes they can hang up and cause that.


A throat is normally short or long / not undersized…
NORMALLY on a factory rifle the free-bore is cut with a standard reamer so all of them are over, or all of them are over (short vs. long)


I would check for burrs on everything, then I’d use a Sharpe market and color the tip of a bullet to see if / where I’m touching lands when shoving the bullet in to see if one of the lands (or all of them) are cutting into the bullet at that point vs. being seated harder.

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You could do a chamber cast with a product called cerrosafe(?) from Brownells, or find a long shaft, bore or hole gauge.

I had same rifle/chambering in the spring of 21. A short or undersized throat. Ruger said they cleaned & polished on the first trip, a no go & in the meantime I'd acquired a modified case to help me check as well.
I was very specific about the problem when I called Ruger the second time & also put a big note in the box. They sent me another ship label. They replaced the barrel that time & ll was well. A few other members here had same issue about that same time.

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They probably used the same reamer until it wouldn't cut anymore.

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Before doing anything further, I'd suggest taking a look with a bore scope to rule out anything obvious.

Good shootin' -Al


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I haven’t thought about a burr. I’ll use the modified case and push the bullet past where I can resistance and see if I can find any scratches.

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Try polishing the bullet with some 0000 steel wool. That helps identify the rifling contact.

Do you have access to a bore scope?


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Odds are, the throat is not undersized but the bullet may be slightly eccentric or the bullet could be oversized. Another issue which can rear it's ugly head, is deflection of the six fluted reamer in a 5 groove barrel. This is not usually an issue when using a reamer with integral throat but if the throat is cut separately it certainly can be.
In this case, the throat is nominally, ..2435" It's likely to be within .0002" of that, plus or minus. It's not unusual to see bullets which are . 2433" or so. The truth is, if you can push the bullet into the throat, with minimal effort, there is no interference fit but it might be close to size on. Shoot it and keep it clean and it ain't gonna get any smaller! GD

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Update- Thanks to all for the replies.

I thoroughly cleaned the chamber and bore. In the bore I used JB bore paste on a flannel patch wrapped around a bronze bore brush and used my drill to polish the inside of the chamber up just past the neck. Finished everything with solvent and then dry patches until clean.

Today I took a factory Hornady 108 grain ELD Match cartridge and measured the OAL at 2.790” Colored the bullet with a black Sharpie, dropped it in the chamber and closed the bolt. Withdrew the round carefully trying to keep it away from the chamber walls.

The bullet had marks from the lands almost all the way back to the case mouth. I did this several times just to verify. So I guess I’ll give Ruger a call on Monday to see what they say.

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Maybe try feeding her a good amount of vodka or tequila and playing some Little River Band or Bee Gees softly in the background


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Originally Posted by cv540
Maybe try feeding her a good amount of vodka or tequila and playing some Little River Band or Bee Gees softly in the background

Yea, that might loosen her up.

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If you have a fired case from that gun measure the outside neck diameter, then measure the neck diameter of the Hornady case. Hornady 11 edition shows a neck diameter of .275, your fired case should be within 3-4 thousands of that, if not 5-6. If that Hornady case gauge is close to that .275 number it might not be opening up enough to get a proper measurement and putting marks on the bullet as well. If any doubts take the same marker to the neck of the Hornady case.

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Originally Posted by Jim270
If you have a fired case from that gun measure the outside neck diameter, then measure the neck diameter of the Hornady case. Hornady 11 edition shows a neck diameter of .275, your fired case should be within 3-4 thousands of that, if not 5-6. If that Hornady case gauge is close to that .275 number it might not be opening up enough to get a proper measurement and putting marks on the bullet as well. If any doubts take the same marker to the neck of the Hornady case.

Just measured the fired case and the OD is .275”. Then measured the Hornady modified case and OD is .273”. The modified case slides into the chamber easily and a bullet moves freely in and out of the case.

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A SAMMI spec chamber will have a .2435 diameter freebore with a length of right at .183. After that, there's a 1°30 leade angle over a fairly long transition length.

So, it wouldn't be hard to get faked out using the Hornady tool.

I'd suggest using the stripped bolt method to establish the 'touch point' for the bullet. Then, with the same bullet, try the Hornady tool and compare the two.

Good shootin' -Al


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Originally Posted by Houser52
I been loading for a long time but haven’t run across this before. The rifle is a Ruger American Predator 6mm Creedmoor.

To determine bullet seating depth I do like a lot of folks, using a Stoney Point gauge, insert bullet in the modified case, slide into chamber, move bullet forward until it touches the lands and start adjusting COAL from there.

What I’ve run into is what I think is a tight throat. After inserting the modified case into the chamber and start to move the bullet forward, I feel substantial resistance after only a few thousandths then I can push it on in to a hard stop which is I assume to be the lands.

Is there anyway to determine if the throat is undersized?


Sounds to me like your "Modified" piece of brass is grabbing the bullet pretty hard. The bolt is nothing compared to a press for seating bullets and you will encounter some notable friction there. If you can't slide the bullet in and out of the neck by hand its to tight


Trystan


Good bullets properly placed always work, but not everyone knows what good bullets are, or can reliably place them in the field
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How many lands and grooves in that barrel? GD

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Trystan- The Hornady modified case is the one that Hornady sells and all bullets slide in and out of the case freely, no drag whatsoever. That’s not the problem.


The bullet is definitely touching something else before contacting the lands. I tried something that was mentioned elsewhere…

inserted the bullet into the modified case, then inserted that into the chamber, turned the rifle muzzle down and let the bullet fall on its own down into the throat until it stopped, then lower the comparator rod and locked it in place. Tried this several times and took measurements and it looks like the bullet never makes it to the lands.

Max OAL is supposed to be 2.800” and each time it was anywhere from 2.500”- 2.650” OAL. As I mentioned earlier, I can push the bullet past the first time it stops into the lands.

I don’t have access to a bore scope or I’d take a look.



Grey dog- the rifle has 5 grooves

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Ruger has had problems with short throats on their 6mm Creedmoors, with several instances reported on this forum in the past few years. Call Ruger and they should send you a label to ship the rifle back to the mother ship.

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Originally Posted by prairie_goat
Ruger has had problems with short throats on their 6mm Creedmoors. There have been several instances reported on this forum in the past few years. Call Ruger and they should send you a label to ship the rifle back to the mother ship.

Yep, I think I’m going to give Ruger a call and send it in and have them check it out.

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I have seen a number of five groove barrels in which the throat is defective, due to reamer deflection. In these barrels, there is evidence that the reamer has cut in the grooves but has not fully removed the lands. This is the result of one cutting edge of the reamer being unsupported by the others. The reamer essentially bounces back and forth as it cuts. This phenomena is made worse if the reamer is a bit dull. As I said earlier, this is most common when the throat is cut separately but it does happen with reamers which have an integral throater as well. The deflection is not huge, and to the naked eye, the throat appears normal. The amount of deflection is probably on the order of .001" or slightly less but it is still enough to leave enough land to contact the bullet. If one has the ability, it is possible to detect the deflection in the neck as well. In a throat which has this defect, the functional diameter of the throat will be somewhere near nominal bullet diameter or just a little less.
Is it correctable? Yes, it is. The use of a spiral fluted throater, or a five fluted throater, will allow one to remove the remaining tops of the lands. The throat will still be a little weird because the grooves will but radiused differently than they should be, but the throat will work out OK.
I have to emphasize, with the right tooling, the right set up, and the right technique, this will not happen. It is my opinion though, Ruger has an issue in one or more of these areas; at least in this chambering. GD

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