.308 Chamber Length Normal/Not-Normal

[jarhead1077]

I own a Model 10 FCP HS Precision in .308., 24 " barrel, with about 350 rounds through it. The following was noted:

Using Hornady Length gauge with SMK 175 (GM308M2) bullet the following measurement is made to ogive = 2.209.
Using same comparator the SMK 175 (factory loaded round) is average 2.223 to ogive.
That would mean that I am jamming into the lands 0.014
The SMK 168 is average 2.228 to ogvie which would mean jamming into the lands 0.019
When I load a 175 SMK round into chamber with bolt and eject, I can clearly see the 6 lands mark below where the comparator ogive is realized on the bullet. If I make an eyeball measurement to just where the land marks "start", I get a measurement of 2.209.
The new once fired brass does not show signs of over pressurization for any of the normal clues.
The 175 SMK shoots as low as 0.471 five shot group at 100 and less than 0.7 five shot group at 300.
If reloading is attempted it seems that backing the bullet off the lands will shorten the case volume respectively.
The COAL for the new GM308M2 175 SMK is average 2.801 with ogive measurement average of 2.223 (Average of ten with high/low not considered)

Question#1: Is this by design and intentional?
Question#2: Do I have a more than normal short chamber? (Kissing the lands at 2.787 effectively)

[Robinhood]

Just a thought.
#1 Did you compare the case head space of you Hornady Modified Case against your factory loaded rds case head space? I realize this is not an answer but if you are dealing with 3 digits behind the decimal it is part of the equation.
#2 Your chamber is not short, your throat is. This can be fixed by a competent smith.

[jarhead1077]

Case head space from the Federal unfired brass, to the once fired brass, to the modified brass were all within 0.001 of each other.

Thanks for the correction on short throat.

[Robinhood]

Your measurements with your LNL gauge is comparable to your factory ammo then. Many have had this same issue with this caliber of Savages.. As far as the ammo is concerned the loads are not hot.

[jarhead1077]

So I either live with short throat (continue to shoot factory load) or
load to measured length starting at the lands with light loads working up or
have a gunsmith lengthen throat?

[FW Conch]

^ or contact Savage and see if they agree that your chamber is not to speck. With as much as we are hearing this happen I would think they are familiar with the problem. They may take care of it for you. As time goes on and you get bitten deeper by the bug, you'll be sending a dummy round along with your barrel order to be throated to your exact specks, as many here do. Until then, your stock Savage rifle should safely chamber Factory loaded ammo. ^

[jarhead1077]

Contacted Savage and they replied verbally the legal response about meeting SAAMI specifications. Have initiated a written request and patiently waiting on response. What does the average costs range for reworking with dummy round? How would I establish the dummy round if shooting around 0.5 to 0.6 moa into the lands right now? Would I shoot some ladder strings with bullet set deeper and starting with lower powder charge working up?

[FW Conch]

Would be interested to hear the response from Savage.

Can't speak to the cost of gun smithing in your area.

Minute Of Angle (MOA), refers to the amount a bullets impact is off the point of aim, or the spread of a group of shouts fired. One minute of angle is about 1" at 100yds. The distance the bullet is set from the lands is measured in thousands of an inch, and is an adjustment made at some point in the loading process in an attempt to make the MOA of the shots(group) fired as small as possible.

To have a chamber re throated, I would decide on the longest bullet I want to shoot, load it at least one bullet diameter of bearing surface in an empty case, and add in thousands the amount I want it off the lands. This is the amount of throat the gunsmith would add to the chamber. Whee! I think I said all that right?

But with your level of experience right now, I would shoot factory ammo that will properly chamber in your barrel, or load according to the throat you have, as has been suggested by others. This, assuming that Savage doesn't offer you a solution. Rethroating or replacing the barrel can be done later as you gain more experience.

I will say it very plainly. IMHO, a factory rifle barrel that cannot chamber a factory loaded cartridge that is to SAMMI speck, without jamming in the lands, IS THROATED TOO SHORT ! Best of Luck

Edit: If that proves to be the case, how you handle it is your choice.

[jarhead1077]

I really appreciate the information for sure. I am sure I will hear from Savage eventually with my written request.

Sorry wasn't very explanatory from my reply/post at 2139 hrs CST

I measured the factory Federal 175 gr SMK HPBT chambered 0.014" on average into the lands. Shooting 0.5 to 0.6 moa at 100 yds out to 300 yds with five shot groups. When chambering round the bolt seems to close with just normal force. No problem ejecting.

I will update when the vendor response is known.

[culpeper]

That 2.228 is the same as I get with the 168SMK (Model 12 Varmint). The throat is a little short so I load 1/32" back and shoots fine. Problem is FGMM is no go on a dirty barrel. It will pull the bullet right out the case. I've had the rifle almost 2 years with 1200 rounds down. Still tight. So, COAL is about 2.81 right into the lands to date and from day one. I shoot COAL 2.778. Rifle accuracy is a confirmed .65 moa 90% of the time on a non overheated barrel (10 shots under 5 minutes). That is the only reason I don't send it back. When I rebarrel I will fix the issue. So, as mentioned by Savage it is within specs just not the sloppy specs we are used to from a factory rifle. Obviously, the FGMM is for over throated factory R700s. :) BTW, no signs of over pressure jammed into the lands but doesn't shoot any better. Thus, I just back off a little for easy chambering. Still doesn't explain the 3" magazine useful length. Hope this helps.

[jarhead1077]

It does help, thanks culpeper for reassuring me on your short throat also. All things considered my COAL of 2.787 or ogive comparator 2.228 with 168 SMK is seemingly a copy of your short throat.
Question: Did you get any feedback from Savage also (verbally or by request?)?
Question: Did you also shoot factory 168 SMK from Federal when new, and only found out that they were in the lands when you measured for reloading?

[culpeper]

I ran 500 rounds at 2.830 that fouled the barrel up pretty good. Next time out I couldn't get these to chamber. So I tried chambering an FGMM 168SMK and it pulled the bullet out. I tried another one same thing. Cleaned the barrel good and tried again it would chamber but nicely into the lands. Went back to 2.78 with no problems. I didn't bother contacting Savage because they would just say it is within SAAMI specs (which is what happened to you). Max seating depth for 168SMK is about .51. That would leave about 2.703 COAL, which is well within specs. Since it is a plain jane factory rifle shooting sub moa I'm good. I bored scoped it and it is got a lot of miles still to go.