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Discussion Starter · #1 ·
It lies.

When starting to reload 6.8 before my Sinclair guage arrived I used a new Crafstman socket that the case would slip into and the shoulder bottom out on the area between the square drive portion and the 12 point socket portion. This allowed me to measure the length between the base of the case and the shoulder before and after resizing. I set my press up to bump the shoulder about .003" to .004". (I had not heard of using a 9mm case).

When the Sinclair arrived and the case pre and post resizing were measured, the apparent bump was between .007" and .009" and the dies were readjusted to give a .003" to .004" bump.

Recently I talked to Constructor on the phone and the subject of longer than mag length came up. He mentioned that it was possible to try longer lengths without modifying a mag by single loading.

So, I loaded 5 rounds of 120SST with 28.4 gr of H322 @ 2.295" and 5 rounds with the same charge @ 2.30".

At the range the 2.295" rounds were fired by loading a single round in the mag, getting the rest and sandbags positioned to put the scope on target and then closing the bolt. The round would then be fired within 10-20 seconds. A minute or two wait between shots and repeat.

When it came to the 2.30" rounds, an empty mag was inserted and a single round was placed in the chamber. Pulled back on the charging handle and allowed the bolt to go about 1/3 forward and the handle released. Sand bags positioned and 'CLICK'. WTF? Wait a minute or longer with rifle pointed down range and pull back on charging handle. No Go! Rifle is not fully into battery. Forward assist won't close the bolt and charging handle won't open the bolt.

Once home and after opening the bolt with a tool through the mag well the investigation revealed that the shoulder was not being bumped at all despite the Sinclair gauge indicating it was. This was confirmed with a 9mm case. The Sinclair guage does not have a radius between the bore for the neck and the shoulder. The fired case does. When the case is resized the neck is a few thou smaller diameter including the portion with the radius. The smaller diameter of the radius on the resized case slips further into the Sinclair guage and gives a false reading of a shoulder bump. The guage is not taking it's measurement from the angled portion of the shoulder, but from the radius between the neck and the shoulder.

I confirmed this by backing my die up .004" and resizing a fired case. The guage still gave a reading of a .003" shoulder bump. A sharpie mark was placed on the neck and shoulder transition of the case and the case inserted and spun in the Sinclair guage. The sharpie mark was removed in a very narrow line on the radius between the neck and shoulder.

I had to adjust my die down approx .008" from the setting the Sinclair guage indicated was giving a .004" bump to obtain a measured bump of .003" using a 9mm case.

The case with a .003" bump was placed in the chamber and the bolt allowed to close from about 1/2 stroke and the bolt closed and opened without issue.

Methinks a 9mm case with a value of about 2¢ does a better job than the guage I spent about $20 on.

I haven't had a chance to see if the 2.30" oal rounds are more accurate than the mag length rounds.
 

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It lies.

When starting to reload 6.8 before my Sinclair guage arrived I used a new Crafstman socket that the case would slip into and the shoulder bottom out on the area between the square drive portion and the 12 point socket portion. This allowed me to measure the length between the base of the case and the shoulder before and after resizing. I set my press up to bump the shoulder about .003" to .004". (I had not heard of using a 9mm case).

When the Sinclair arrived and the case pre and post resizing were measured, the apparent bump was between .007" and .009" and the dies were readjusted to give a .003" to .004" bump.

Recently I talked to Constructor on the phone and the subject of longer than mag length came up. He mentioned that it was possible to try longer lengths without modifying a mag by single loading.

So, I loaded 5 rounds of 120SST with 28.4 gr of H322 @ 2.295" and 5 rounds with the same charge @ 2.30".

At the range the 2.295" rounds were fired by loading a single round in the mag, getting the rest and sandbags positioned to put the scope on target and then closing the bolt. The round would then be fired within 10-20 seconds. A minute or two wait between shots and repeat.

When it came to the 2.30" rounds, an empty mag was inserted and a single round was placed in the chamber. Pulled back on the charging handle and allowed the bolt to go about 1/3 forward and the handle released. Sand bags positioned and 'CLICK'. WTF? Wait a minute or longer with rifle pointed down range and pull back on charging handle. No Go! Rifle is not fully into battery. Forward assist won't close the bolt and charging handle won't open the bolt.

Once home and after opening the bolt with a tool through the mag well the investigation revealed that the shoulder was not being bumped at all despite the Sinclair gauge indicating it was. This was confirmed with a 9mm case. The Sinclair guage does not have a radius between the bore for the neck and the shoulder. The fired case does. When the case is resized the neck is a few thou smaller diameter including the portion with the radius. The smaller diameter of the radius on the resized case slips further into the Sinclair guage and gives a false reading of a shoulder bump. The guage is not taking it's measurement from the angled portion of the shoulder, but from the radius between the neck and the shoulder.

I confirmed this by backing my die up .004" and resizing a fired case. The guage still gave a reading of a .003" shoulder bump. A sharpie mark was placed on the neck and shoulder transition of the case and the case inserted and spun in the Sinclair guage. The sharpie mark was removed in a very narrow line on the radius between the neck and shoulder.

I had to adjust my die down approx .008" from the setting the Sinclair guage indicated was giving a .004" bump to obtain a measured bump of .003" using a 9mm case.

The case with a .003" bump was placed in the chamber and the bolt allowed to close from about 1/2 stroke and the bolt closed and opened without issue.

Methinks a 9mm case with a value of about 2¢ does a better job than the guage I spent about $20 on.

I haven't had a chance to see if the 2.30" oal rounds are more accurate than the mag length rounds.
I'v seemed to have had kind of the same problem but I'm not sure if it's the Sinclair gauges or the Dies I'm using not being able to fully resize the case base all the way with out setting the shoulder back to far.
My shoulder set back with Sinclair bump gauge .003/.004 will chamber with full bolt slam but you won't un-chamber the un-fired round with out a good lick/hit on the charging handle with a boot heal or rubber mallet... Fired rounds clock out at around 3:00/3:30/4:00 with no problem???????
When I get time I'll figure it out............
 

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I don't know the details of the Sinclair gauge (as I use the Hornady ones)..but are you using the correct bushing? ---it should be measuring off a datum line mid shoulder ( the hole should be .360" -- http://www.saami.org/pubresources/cc_drawings/Rifle/6_8mm Remington SPC.pdf, but Hornady uses .350 as a datum point hole diameter )

I wouldn't use the Sinclair gauges due to this statement on their website : " our comparator bodies and are machined to fit particular shoulder angles of cartridges. Rather than measuring to the datum line,"

bump should always be done off the datum line as that's where saami specs come into play,
 

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I don't know the details of the Sinclair gauge (as I use the Hornady ones)..but are you using the correct bushing? ---it should be measuring off a datum line mid shoulder ( the hole should be .360" -- http://www.saami.org/pubresources/cc_drawings/Rifle/6_8mm Remington SPC.pdf, but Hornady uses .350 as a datum point hole diameter )

I wouldn't use the Sinclair gauges due to this statement on their website : " our comparator bodies and are machined to fit particular shoulder angles of cartridges. Rather than measuring to the datum line,"

bump should always be done off the datum line as that's where saami specs come into play,
Now this makes since, (Datum line and not Shoulder angles) I have a set of Hornady gauges also and will give them a try; I was using Sinclair because their made of steel and not so long,,

I went and measured a fired case with both gauges, .042 difference in gauge measurements; data line or angle.. anyway I got a base line measurement........ I resized the same case and remeasured and both gauges read .003 shoulder set back.....
 

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Discussion Starter · #6 ·
I don't know the details of the Sinclair gauge (as I use the Hornady ones)..but are you using the correct bushing? ---it should be measuring off a datum line mid shoulder ( the hole should be .360" -- http://www.saami.org/pubresources/cc_drawings/Rifle/6_8mm Remington SPC.pdf, but Hornady uses .350 as a datum point hole diameter )

I wouldn't use the Sinclair gauges due to this statement on their website : " our comparator bodies and are machined to fit particular shoulder angles of cartridges. Rather than measuring to the datum line,"

bump should always be done off the datum line as that's where saami specs come into play,
Yes,

Correct insert per Sinclair's website and ordered from Sinclair.

The fired case neck fits into the insert with only a couple of thou clearance. The shoulder never makes it to the angled portion of the insert.

Prior to this discovery, all rounds were either loaded by releasing the bolt from lock back or by a normal cycle when firing.

I had not tried what is described in Winty's comment about not being able open the breech with an unfired round until the 'CLICK'. Since then I tried to open the breech after chambering a couple of cases resized with the dies set using the Sinclair and had similar results as Winty.

After setting the die for .003" bump with a 9mm case, unchambering was done without difficulty.

I consider myself lucky that the rifle did not fire when not fully into battery.

I'll not be using the Sinclair gauge again.
 

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Find a Hornady headspace bushing B, it will fit the Sinclair body. I don't know if you can get that one separate, but you may be able to put out a WTB for someone with the set and does not need the B insert.
 

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Well I tried the 9mm case trick today (thanks Rifter from two years ago) and compared it to the Hornady gauge things are the same except today with out touching settings my dies are setting shoulder back at .005 on both gauges?? LOL oh well.....
 

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Discussion Starter · #9 ·
Find a Hornady headspace bushing B, it will fit the Sinclair body. I don't know if you can get that one separate, but you may be able to put out a WTB for someone with the set and does not need the B insert.
Thanks,

Will see if one is around.
 
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