Cracked bolt replacement issues

I was at the range recently and my carbine started to jam up. I chalked it up to not enough lube and dirty ammo. Well after about 15 more rounds it completely jammed shut. Me nor anyone else at the range were able to get it open. I went home and took it apart to get the bolt out and to my surprise there was a hairline fracture on the right locking lug, barely noticeable on top and getting worse towards the bottom. The bolt was a type II, I will upload some pictures of the crack. Seeing the need for replacement I ordered a complete used saginaw bolt off ebay that looked to be in great shape

I take it to mean that you have a complete replacement guts-n-all? Head-space could certainly be the issue, but it could be a firing pin. Since you had cosmoline on the replacement, the pin could be gooked-up a little. Certainly, you need to take it all to pieces and clean it up. Some ammo will have the primer set a tad deeper than others and I don't know if Aguila is in that family. I make sure I set mine no deeper than flush. You may need to "practice" getting the bolt disassembled by-hand, or just spring for a bolt tool....you will be glad you did sooner or later.

I know how even a small burr in the left bolt lug latch area can break a bolt.....been there and done that not too long ago. I tested a bolt by hand and it would slide-in-and-out and rotate, but there was a noticeable slight drag and I just chalked it off to..."it will wear-in". Well...it did not wear-in and I cracked a bolt. During all this, I had a few failure-to-fires and was chalking it off to ammo, but it wasn't. It was that small burr that was obviously "cocking" the bolt off line enough to cause the FTF issue. Once I extracted my head from a deep dark area...I seriously polished-out the burr and all that ammo that did not shoot, shot on the first strike. Make double-sure you have that restriction polished-out and that new bolt will practically fall into place on an empty chamber.

Measuring overall length of the bolt and/or the depth of the face won't tell you anything.

The critical dimension is the distance between the plane of the bolt face and the plane at the rear surface of the right locking lug. That's where the difference in headspace enters when you change bolts.

Absent actual headspace gages, you could measure your Aguila cases to see if they are systematically different from the tulammo and armscor case lengths.

Too short for your chamber and you get light strikes and often no bang.

Too long and you could, IF YOU ARE ONE LUCKY SOB, get the same "light strikes" if the hammer is prevented from fully impacting the firing pin in a bolt not fully locked into battery! If unlucky, I hope you have insurance.

As a minimum I would at least invest in a FIELD GAUGE to check headspace.   Also good to have during the "inspection period" when buying a rifle, especially from an individual..."trust but verify"  On a quick Googlin' I saw a Forster on ebay $29.95 + $2.99 shipping, or the GO and NO-GO for $59.95 + $2.99 shipping. 

Thank you bonnie for the economical alternative to buying all the gauges, I know I have a feeler gauge laying around here somewhere and $25 or $35 is much more doable than buying all three. As for the ammo, without having any empty brass with me I can say this: The cases are all the same height, from an ocular inspection on a level surface (3 groups of 3). The aguila ammo does however have the bullet seated deeper making it about ~1 mm shorter than the armscor or tulammo. One other noticeable difference is the extractor groove on the aguila is much thinner than the other two, not sure if that would effect anything but ejection though.

Using feeler gauges to measure headspace with a Go gauge.
Not my brilliant idea. Learned this from some genuine firearms experts above my pay grade. Never have had an issue. If you want to take the time, you can find out the exact headspace of a particular gun using this method.

I am not opposed to have a set of go, no go, field gauges myself.

blackfish wrote: Brownells sells a chamber length gage for about $6 which will tell you what your EXACT headspace is.

I had not seen those.  Pretty neat!  Why do you think they say,"Should not be used in handguns, semi automatic rifles, lever actions rifles and pump action rifles."?  Lack of force control for loading and ejecting the cartridge?

sling00 wrote: Why do you think they say,"Should not be used in handguns, semi automatic rifles, lever actions rifles and pump action rifles."? Lack of force control for loading and ejecting the cartridge?

That I don't know, never noticed that warning before. Maybe it's because they also have headspace gages they'd rather sell you for 5X the price. As to force control, just remove the springs as you would when using a standard headspace gage (i.e. don't load the gage into the chamber like a cartridge) and I don't see, nor have I encountered, any problem in actual use, for semi-automatic rifles at least. YMMV

Chamber length gauges are not headspace gauges. Chamber length guages are machined to a lesser diameter then the chambers specs to allow them to always reach the point where the chamber ends and the rifling begins in order to get perfection when trimming cases while reloading.  Headspace gauges are machined to near exacting specs of what a chamber should be.  I did recently read a thread about headspace on an old CMP forum where someone said that you could make a no-go guage by wrapping scotch tape over a casing (so many wraps were equal to how ever many thousands of an inch) sounded kinda crazy to me.  

I don't believe this is correct, but I'll measure the 0.336" diameter dimension for this gage myself (it looks the same as the case neck diameter for this caliber - yes, 30 caliber does have a "neck"!)



and the diameter for the associated headspace gages the next time I have access to all my stuff.