Rifle seating depth, overall cartridge length, SAAMI spec and safety
Bob Bethune
loaded to an OAL of 2.8250" will just touch the lands. SAAMI spec says
maximum overall length for .308 Winchester is 2.800 inches. Is a
cartridge loaded to 2.8060" OAL safe in this rifle, even though that
OAL would exceed SAAMI spec? In other words, is my chamber cut a bit
on the generous side?
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Ralph Mowery
"Bob Bethune" <poi...@comcast.net> wrote in message
news:hmsdhs$tt3$1...@news.albasani.net...
# In my Remington 700 VLS chambered for .308 Winchester, a cartridge
# loaded to an OAL of 2.8250" will just touch the lands. SAAMI spec says
# maximum overall length for .308 Winchester is 2.800 inches. Is a
# cartridge loaded to 2.8060" OAL safe in this rifle, even though that
# OAL would exceed SAAMI spec? In other words, is my chamber cut a bit
# on the generous side?
The SAAMI spec is so that all cartridges will chamber and work through the
magazine of a gun. If your gun will take a slightly longer cartridge and
work throughthe action, it is safe for your gun. The spec is sort of like a
maximum cartridge length and mimimum rifle length.
The shape of the bullet could come into play also.
A long skinney bullet may not touch the lands where a round nose bullet
might for the same overall lenght of the round.
You usually only get into trouble by making the overall lenght shorter as
far as not being safe. That mostly hapens with the hand guns . If the
bullet is seated too deep the pressure will rise somewhat. This is
especially true with rounds such as the .40 S&W. The case is almost full of
powder and the round is alaready at almost the maximum pressure. That is
why you probably will not see a +P load for that round.
Doug White
@news.albasani.net:
# In my Remington 700 VLS chambered for .308 Winchester, a cartridge
# loaded to an OAL of 2.8250" will just touch the lands. SAAMI spec says
# maximum overall length for .308 Winchester is 2.800 inches. Is a
# cartridge loaded to 2.8060" OAL safe in this rifle, even though that
# OAL would exceed SAAMI spec? In other words, is my chamber cut a bit
# on the generous side?
Factory chambers are almost always cut long so that ammo loaded to SAAMI
specs will be safe. If you don't know what you are doing, having bullets
touching the lands can cause pressures to increase. If you are single
loading & know how to watch for pressure signs, it is possible to reload &
safely shoot longer rounds than SAAMI recommends. Another issue is that a
given OAL can have very different distances to the rifling, depending on
the exact shape of the bullet. You may find that you can touch the lands
within the SAAMI OAL limits with a different bullet (although I doubt it).
Doug White
Long Ranger
"Bob Bethune" <poi...@comcast.net> wrote in message
news:hmsdhs$tt3$1...@news.albasani.net...
# In my Remington 700 VLS chambered for .308 Winchester, a cartridge
# loaded to an OAL of 2.8250" will just touch the lands. SAAMI spec says
# maximum overall length for .308 Winchester is 2.800 inches. Is a
# cartridge loaded to 2.8060" OAL safe in this rifle, even though that
# OAL would exceed SAAMI spec? In other words, is my chamber cut a bit
# on the generous side?
Most rifles have a bit of freebore and the length of it is subject to the
manufacturers whims. The bullet typically has to "jump" to the rifling.
Extending the cartridge length to engage the rifling typically raises
pressure and reworking your load from the low side up to your current recipe
is highly recommended if you change the seating depth to make contact with
the lands. As far as SAAMI specs go, cartridge overall length is pretty much
adjustable if you take care to follow up with load corrections. The typical
sporting rifle runs out of magazine length before you hit the lands anyway.
Some cartridges, even though they will chamber, end up too long to extract
unless fired.
Michael Medley
the rifling. The shape of the projectile is the key issue here.
Midway reloading has the Stoney Point Ballistic Comparator,
which is a tool that compensates for the different shape in
projectiles.
I had a similar issue with a Ruger 77 that I owned. With long secant
slugs, I could go .200" over the SAAMI OAL and still not touch the
rifling. I was running out of space in the magazine
Manufacturers have cut too much freebore in barrels for over 30 years,
previously they cut too little. From one extreme to the other.
Bob Holtzman
# In my Remington 700 VLS chambered for .308 Winchester, a cartridge
# loaded to an OAL of 2.8250" will just touch the lands. SAAMI spec says
# maximum overall length for .308 Winchester is 2.800 inches. Is a
# cartridge loaded to 2.8060" OAL safe in this rifle, even though that
# OAL would exceed SAAMI spec? In other words, is my chamber cut a bit
# on the generous side?
Believe me, .006" will make no difference.
John Kepler
# In my Remington 700 VLS chambered for .308 Winchester, a cartridge
# loaded to an OAL of 2.8250" will just touch the lands. SAAMI spec says
# maximum overall length for .308 Winchester is 2.800 inches. Is a
# cartridge loaded to 2.8060" OAL safe in this rifle, even though that
# OAL would exceed SAAMI spec?
There HAS to be a spec at some point, and in some applications, that
2.800" is a rigid "hold" value (like if you are loading for a magazine-
fed gas-gun....use an M14 as an example), if only because if you load
any longer, the round won't feed or necessarily fit in the magazine.
However, that isn't the case in your rifle.
"Loading long" is something almost every competition shooter
does....you simply can't compete with an AR/.223 combo and load to
SAAMI-spec OACL in certains portions of the shooting course.....ditto
for almost ANY Long Range competition. With some provisos, it's safe
and effective.
Now for the "provisos".
"Loading Long" increases peak bore pressure, and you MUST work-up your
loads accordingly. A load that worked just fine with a "short" OACL
can be giving over-pressure signs when "loaded long". Be
conservative, be attentive in your work-ups....a chronograph is nearly
a must (if your velocities are unexpectedly high, your pressures
probably are too!), and you'll generate a much more accurate,
perfectly safe load custom-fitted to your rifle.
Second, and one where I feel you already have a problem....find out
how long your throat/leade actually is using a Stony Point Gauge or
equivalent. The numbers you have provided for your rifle sound fishy
already....if your numbers are correct, you've got a throat/leade
shorter than my custom-built Palma competition rifle (unlikely!).
Obtaining a correct throat/leade length will help you determine the
best OACL for your rifle. In my experience, 0.020" off the lands is
the best compromise between pressure and performance, YMMV! Also, you
should set your OACL with an ogive comparitor rather than a simple
"base-to-tip" measurement....even the very best match pills vary in
length when measured that way which can really mess-up that more
critical lhroat/leade engagement distance, but not when measuring base-
to-ogive.
In other words, is my chamber cut a bit
# on the generous side?
Bud....lawyers NEVER sleep, and no one requires a competency test to
buy reloading equipment! Virually all commercial firearms produced in
the last 30 years have ridiculously long leades to cover the
manufactures a$$....it's a "matched set" with the 10 lb. "lawyer
triggers" everyone knows and "loves"!
John
#> ------------------------------------------------------------
Rubaiyat of Omar Bradley
# "Loading Long" increases peak bore pressure, and you MUST work-up your
# loads accordingly. �A load that worked just fine with a "short" OACL
# can be giving over-pressure signs when "loaded long".
Can you elaborate on why that is so - it seems counter-intuitive. I
would have thought that loading long, provided that the bullet is not
touching the lands, ought to produce less pressure rather than more
pressure.
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Jim
"Rubaiyat of Omar Bradley" <cowar...@yahoo.com> wrote in message
news:hn1pkt$o4s$1...@news.albasani.net...
# On Mar 6, 5:36 am, John Kepler <jekep...@amplex.net> wrote:
# # "Loading Long" increases peak bore pressure, and you MUST work-up your
# # loads accordingly. A load that worked just fine with a "short" OACL
# # can be giving over-pressure signs when "loaded long".
#
# Can you elaborate on why that is so - it seems counter-intuitive. I
# would have thought that loading long, provided that the bullet is not
# touching the lands, ought to produce less pressure rather than more
# pressure.
The shorter the jump-time to the lands, the less gas is allowed to pass,
increasing pressures.
Long Ranger
According to the teachings I've had, it has more to do with momentum. The
bullet achieves enough momentum in it's initial movement as it clears the
distance to fully engaging the rifling. If it is right up against the
rifling when started, pressure can build to dangerous levels before the
bullet has a chance to move and overcome it's resting inertia. This is the
same thing that happens when a low-powered handgun round "detonates".
Allegedly the primer pressure sets the bullet up in the forcing cone, then
the charge pressure comes and since the bullet is "stuck" there, and has no
forward speed, it can't get out of the way of the pressure wave fast enough.
You can increase pressure in rifle rounds by deeper seating too. If you can
imagine a graph of these two phenomena superimposed, there would probably be
overlap between the two different scenarios. As you let the bullet out of
the case and made it longer, the pressure would drop, and as you approached
another point, it would start going back up based on the situation described
above.
Natman
#increasing pressures.
#
Allowed to pass? The bullet hasn't left the case neck yet, what (got
to be careful here) gas is passing?
Louis Boyd
# #The shorter the jump-time to the lands, the less gas is allowed to pass,
# #increasing pressures.
# #
# Allowed to pass? The bullet hasn't left the case neck yet, what (got
Yes, that can happen. I was experimenting with a Thompson Contender
300 Whisper barrel with 220 grain Sierra Matchkings seated deep in the
case using a small charge of fast powder. The jump to the lands was
about 1/4 inch. On firing all of the propellant gas passed between the
case neck and the bullet then exited the barrel before the bullet moved
forward enough to engrave in the lands at all. While there was a
moderately loud report the bullet simply fell out of the barrel (breech
end) when the cartridge was extracted.
That was an extreme case, but for small cases with heavy bullets
propellant loss prior to engraving can be a major cause of poor velocity
uniformity. The case neck will open up to the size of the chamber
neck long before the bullet leaves the neck area, at least when fast
powders are used. Tight neck chambers help but don't eliminate the
propellant blow by. Seating the bullet into the lands can eliminate
blow by but can also cause high and variable pressure spikes which
depend on the pressure which must be achieved before the bullet moves
further which also hurt velocity uniformity.
Load development is a tricky business when trying to achieve very low
velocity spread. There is not a right answer to the optimum bullet
seating depth and distance to the lands. Large jump is rarely good for
accuracy but finding what seating depth is best for a particular
rifle/bullet/powder is part of the joy (and misery) of load development.
Long Ranger
"Natman" <nat_...@yahoo.com> wrote in message
news:hn2p9f$8qf$1...@news.albasani.net...
# #The shorter the jump-time to the lands, the less gas is allowed to pass,
# #increasing pressures.
# #
# Allowed to pass? The bullet hasn't left the case neck yet, what (got
# to be careful here) gas is passing?
He's right that some gas passes the bullet as it makes that jump, but I
don't think it's significant to the pressure being generated. I read that
and wondered if the poster was imagining that the bullet was actually free
of any contact at some point during that "jump". It obviously engages the
rifling before it clears the case neck, but it is in an oversized part of
the bore, and the case neck swells into it's part of the bore leaving a tiny
gap around the bullet for a minute part of it's travel. It's also my
understanding that a bit of gas gets past the bullet all the way down the
barrel too, but again, not enough to make a difference in an over-pressured
load.
Jim
"Long Ranger" <worp...@comcast.net> wrote in message
news:hn38t7$3ap$1...@news.albasani.net...
# He's right that some gas passes the bullet as it makes that jump, but I
# don't think it's significant to the pressure being generated. I read that
# and wondered if the poster was imagining that the bullet was actually free
# of any contact at some point during that "jump".
No, not free of contact, but there are a few microseconds before the case
expands to seal the chamber and the bullet seals in the grooves that allows
for some gas escapage. Making rounds longer essentially makes the chamber
shorter.
Natman
<bo...@apt0.sao.arizona.edu> wrote:
> ...
Well, yes, if you have a 1/4" of freebore things might well be
different. The OP was talking about .06", not .25!
Sp...@controlq.com
# Date: Sat, 6 Mar 2010 02:10:05 +0000 (UTC)
# From: Bob Bethune <poi...@comcast.net>
# Newsgroups: rec.guns
# Subject: Rifle seating depth, overall cartridge length, SAAMI spec and safety
#
# In my Remington 700 VLS chambered for .308 Winchester, a cartridge
# loaded to an OAL of 2.8250" will just touch the lands. SAAMI spec says
# maximum overall length for .308 Winchester is 2.800 inches. Is a
# cartridge loaded to 2.8060" OAL safe in this rifle, even though that
# OAL would exceed SAAMI spec? In other words, is my chamber cut a bit
# on the generous side?
#
Sinclair carries a number of guages to measure ogive length to rifling,
and are a good idea if you want to experiment. Note that the most
accurate guages require actual brass, and the actual bullet, and involve
measuring the OAL to put the ogive *RIGHT INTO the LANDS*. You probably
want to back off that measurement a couple of thou' minimum, but accuracy
freaks vary as to just how far off the lands your loads should be. This
may also vary from one rifle/calibre/bbl to another.
HTH,
Rob Sciuk
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Louis Boyd
# On Mon, 8 Mar 2010 16:33:40 +0000 (UTC), Louis Boyd
# <bo...@apt0.sao.arizona.edu> wrote:
#
# > ...
#
# Well, yes, if you have a 1/4" of freebore things might well be
# different. The OP was talking about .06", not .25!
#
But the same principle applies. Are you happy if you only loose 20% of
the propellant gas out the barrel before the bullet engraves?
Natman
<bo...@apt0.sao.arizona.edu> wrote:
#Natman wrote:
## On Mon, 8 Mar 2010 16:33:40 +0000 (UTC), Louis Boyd
## <bo...@apt0.sao.arizona.edu> wrote:
##
## > ...
##
## Well, yes, if you have a 1/4" of freebore things might well be
## different. The OP was talking about .06", not .25!
##
#But the same principle applies. Are you happy if you only loose 20% of
#the propellant gas out the barrel before the bullet engraves?
#
#
????
I'm afraid I don't understand your post.
My point is that if the bullet only has to move a few hundredths to
engage the rifling, the base of the bullet will still be inside the
case neck, therefore no gas will escape.
sta...@prolynx.com
leading to gas escaping before the bullet moves much. There's been a
lot of photos done of this "young gas" escaping prior to bullet
engraving and sealing off things. Some of the articles I've read said
that barrel erosion was mostly caused by this gas escape, being high
pressure, high temperature and high velocity. It can also damage the
bullet base and affect accuracy. Lead bullets can have the base
washed away and deposited up the bore, too. Have had that happen a
few occasions.
Stan
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Ledgewalker
it, and either way, it goes to show, even a pre-gezzer can learn
something. Appreciate the flow, beats getting upset over cable news...
Ray, aka RMR
(Si vis pacem
para bellum)
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Jim
"Natman" <nat_...@yahoo.com> wrote in message
news:hn63kq$rgr$1...@news.albasani.net...
# My point is that if the bullet only has to move a few hundredths to
# engage the rifling, the base of the bullet will still be inside the
# case neck, therefore no gas will escape.
Gas starts leaking before the bullet moves, as the neck expands to meet the
chamber wall.
Natman
#
#
#"Natman" <nat_...@yahoo.com> wrote in message
#news:hn63kq$rgr$1...@news.albasani.net...
## My point is that if the bullet only has to move a few hundredths to
## engage the rifling, the base of the bullet will still be inside the
## case neck, therefore no gas will escape.
#
#
#Gas starts leaking before the bullet moves, as the neck expands to meet the
#chamber wall.
#
#
Ah, makes much more sense now. Thanks.