RCBS precision mic gauge

[ulen mn]

I was messuring the headspace of twice fired brass with the RCBS precision mic gauge and found that my brass comes in .002 less than sammi standards ( mine is 1.5593 sammi is 1.5613 to 1.5713 ) I also pulled apart two hornady factory loads and they also come in at 1.5593 out of the box. Now is it possible to have that tight of a chamber in a factory CZ 527 varmint that the headspace is not expanding????? Or am I reading something wrong here? I am new to handloading and learning as I go by reading , asking questions, this site by far has the most answers than anywhere I have looked alot of time I dont have to ask the question it is already in a post somewhere here all you guys (and Gals if there are some and I'm sure there are) are great thanks for the help and keep posting. If the post of this site were put into book for I think someone would have a best seller among the handloading community. Thanks in advanced for everyones imput on this question Ulen MN. BY the way I messured after I neck sized the brass was that right or wrong?

[fredbeer]

ulen mn, I have found the same to be true with my Savage 12 Fv. It is below the 0 by .002. Had a Howa and it was below 0 also. This is with brass fired from each rifle. I wonder if the data on the mic may be off. Or there are alot of tight chambers out there.

[jo191145]

ulen mn
This twice fired brass, was it factory loaded for the first firing or new bulk brass you reloaded twice?
By the numbers I'm quessing its factory Hornady loads.
Its very odd that an unfired Hornady would measure exactly the same as a twice fired piece from your chamber. Factory ammo is loaded with some stout charges and should have no problem moving those shoulders.

Do you have any other types of fired brass to compare?

[ulen mn]

This brass is factory loaded for the first firing and hand loaded for the second firing I also have found that the mock bullet and a dummy round have a big difference in length when messuring chamber length to the lands and grooves ( Dummy round messures 2.68 and RCBS mock round messures 1.93 using the sinclair bullet comparator that silver fox recomended and a calliper. RCBS gauge that I have no idea on what lenth zero is comes out at dummy round .208 and the mock round at .1525 ) this leads me to believe that the guage is screwed up or I am really not understanding the RCBS product. I think I will go with 2.68 and go back a little from there for bullet seating it sounds more resonable to me.

Ulen MN

[Silverfox]

Ulen MN--You really have me puzzled with the following statement:

I also have found that the mock bullet and a dummy round have a big difference in length when messuring chamber length to the lands and grooves ( Dummy round messures 2.68 and RCBS mock round messures 1.93 using the sinclair bullet comparator that silver fox recomended and a calliper. RCBS gauge that I have no idea on what lenth zero is comes out at dummy round .208 and the mock round at .1525 )

Is the following picture the tool you are talking about when you mention "measuring chamber length to lands and grooves?"



If so, there will definitely be a big difference in the chamber length measurement using the Sinclair chamber length gauge and the measurement you get when you use the Stoney Point device and slip a bullet into that and then push it into your chamber and then measure that length with the comparator on your caliper.

The Sinclair chamber length gauge insert will stop at the very beginning of the lands, whereas the bullet your push into your chamber with the Stoney Point device will allow the bullet to come into contact with the lands and at that point the nose of the bullet will be well into your barrel. Here's the Stoney Point device I use. You need a "modified casing" which you screw onto the end of the Chamber-All tool. Then you place a bullet into the open mouth of the casing, slide the modified casing into the chamber and get it set in the chamber, and then push the bullet into the barrel with the push rod so the ogive meets the lands. Then you tighten the set screw on the push rod, remove the device and bullet and then with the comparator with the proper caliber insert fastened to your caliper, you measure the distance from the base of the casing to the ogive of the bullet:



Please show us a picture of what you are calling your "Dummy Round" and also show us what you refer to as an "RCBS mock round." I am also puzzled as to what this "RCBS gauge" is as well.

What kind of comparator are you using?? I recommended the Stoney Point type comparator to you. Did you buy this one pictured below?? It is the "nut" type in the little inset picture on the lower left-hand corner of the photo.



If that's the one you purchased, that IS NOT what I suggested you buy. I urged you to get one like this:

[ulen mn]

Silverfox I did purchace the one you recomended sinclclair part #09-1000 and 09-0204 I do not have a digital camera any more ( daughter barrowed it 4 months ago havent seen it since) what I call a dummy round is a 204 case with a bullet seated shallow then I put it in the chamber and closed the bolt pushing the bullet back into the neck of the case when it hit the lands and grooves . The RCBS mock bullet is a 204 case ( only smaller in diamiter than a normal case ) without the neck and shoulder, and has a plastic insert with what resembles a 204 bullet on top, you tighten a set screw in the case that makes the plastic insert tight and chamber the round and it is supposed to give you the length from your bolt face to the lands and grooves ( chamber length right ?? )... Here is what I have with a picture of from the RCBS web site. https://shop.rcbs.com/WebConnect/,DanaI ... uctId=3186

[ulen mn]

Sorry for some reason the link shortend itself when i pasted it into my message.... And Silverfox I owe you a appoligy the personal E-Mail I sent was asking about bullet overall length and I did buy the product you recommended
Maybe what I baught and what I have cannot be used together although it looks like it should be able to inter change. ULEN MN

[ulen mn]

O.K. I think I have figured out my problem here it is not the product it is me while out shoveling the 8" of snow we got yesterday and this morning it kinda hit me. I am messuring from the ogive to the back of the rim to find out how far I can seat the bullet out and work it back in to find my sweet spot so I came in and chamered the RCBS mock bullet 6 times and came up with a 1.903 and then chambered my home made dummy bullet 6 times and came up with 1.984 difference of 0.081, I thought about this difference and removed the 32gn v-max and tried a 32gn seirra bk but the bullet kept getting stuck in the lands and grooves so I tried a 35gn berger same thing kept gettting stuck, after thinking I remembered that some of you messure your bullets and sort them so I messured 3 of each the v-max came out at 0.209, 0.209, 0.210 the bk's were 0.189, 0.182, 0.180 and finally the 35's were 0.173, 0.171, 0.172. So I think and someone correct me if I am wrong please the v-maxes I will be able to seat close to the lands and grooves the others will be a little farther away to get them seated into the case far enough to not fall out if they are bumped????

[Robert harrel]

i may be wrong but i thought the sinclair chamber gauge just measured the brass chamber length so you know how long your brass needs to be trimmed to then after the chamber you have some freebore and then the lands